If you are looking for extensibility for a fashion doll then Smart Doll is what you would be looking for.

 

View more at www.dannychoo.com/en/post/27360/Mirai+Pulse.html

"The hummingbird, also known as hummingbird, cuitelo, suck flower, pink-flower, suck honey, binga, Guanambi, guinumbi, guainumbi, guanumbi [1] and mainoĩ, [2] is a Trochilidae family bird, composed 108 genera and 322 known species. In Brazil, some genres are given other names, such as tails-white genre Phaethornis or straight-nozzles Heliomaster genre. In the classificatory system of Sibley & Ahlquist, the Trochilidae family was part of a proper order, the Apodiformes. Among the group's distinctive features include the elongated beak, food-based nectar, eight pairs of ribs, fourteen to fifteen cervical vertebrae, iridescent plumage and an extensible and bifurcated tongue".Fonte Wikipédia

So, what is it different from a huge number of other aircraft tugs? To date, this is the first and only representative of the fourth generation because, of course, the best. When we first met, he immediately strike dimensions: length 14.5 m, width of 4.35 m and a height of 2.32 m (without exhaust system) weight of the truck is 70 tons. From him and breathes inside hidden power. And really – his eight-cylinder turbo diesel 12 liters develops immodest 1550 HP Thanks to this power and the latest double-circuit transmission MAT is able to move with a full load at a speed of 25 km/h. For comparison, the maximum speed of most existing tractors under load does not exceed 10 km/h Maximum speed without load is 60 km/h. Such a high rate (at standard tractors it is twice less) allows the machine to quickly and autonomously change their location, especially if to remember its weight and dimensions. Standard ground clearance of the machine is only 14 cm, but the developer is going to release sarojadevi off-road version. Despite the impressive size, the MAT has a high maneuverability thanks to its independent front and rear steering. The new system of smooth adjustment of the angle of the course allows us to reduce the load on the tires when maneuvering and significantly increase their service life. Speaking of tires – even this would not have happened without the revolutionary technologies! They are made from the latest super wear-resistant material – nitrofuranto. Its main feature is the nonlinear elasticity, so engineers were able to abandon the conventional hydraulic suspension and saved so much space and weight. In particular, a tank for hydraulic and, accordingly, oil consumption were reduced by 30%.

 

The MAT is equipped with two reeving winches, which are able to operate in tap mode in the presence of the outer boom. To ensure stability in the tap mode, and to simplify maintenance (try replacing the wheel with a diameter of 1.8 meters at a 70-ton machine), the machine is equipped with hydraulic full-lift jacks. The winch shafts structurally integrated into the carrying frame of the tractor, ensuring reliable operation and safety.

 

The MAT is freely extensible platform. In the front of the machine removed oil seals for hydraulic connections, and at the rear of additional mechanical drive. The manufacturer offers as attachments huge blade and the outer jib-crane. Dozer will be especially useful in winter, as the performance of such a machine an order of magnitude greater than that of conventional snow removal equipment. Because the blade is completely beyond the operator's line of sight, the cabin is equipped with hydraulic lifting devices.

 

Needless to say, the cab operators meet the most modern standards of ergonomics. The touch pad, robotic CAT, review FullHD camera, sound insulation, climate control – everything is done for the best possible experience. Controls the main and auxiliary cabins are fully duplicated, so that the control can be done from any location.

 

Now, when I talked a bit about the original (photos, unfortunately, are not), you can go to my model. Scale 1:19, just under tech-figure. Accordingly, the following model dimensions: length without attachment – 76,5 cm, width (without/with mirrors) – 23/26 cm, height (without/with exhaust pipes) – 13/15 cm, weight – 4,45 kg. On creation took about a month and a half.

www.doublebrick.ru/forums/viewtopic.php?t=55226

Prendre le minou comme la samle à introduire

    

telephone.pascherenchine.com/products/minnie-mouse-beauco...

via Modebas.fr modebas.fr/socquettes/2103-pack-de-12-paires-socquettes-a...

Stout, snout blunt, low crest along back. All green (young) or green with wide brown or blue-green bands; large black-edged scale below ear; extensible throat fan. Tail long, tapering. Can run upright on hindlegs. Looks frightening but is a docile vegetarian. Introduced from Central America. Habitat: Large trees, grassy areas, towns.

Bit of a landmark here, sensation-seekers. I'm beginning the serious transition to Adobe Lightroom for photo editing and library management. I still love Aperture, but Apple's killed it. Apple's new architecture for organizing, editing, and syncing photos hasn't been released yet, so it feels like a good time to do at least one big project with Aperture's competitor. Who knows...I might switch to it permanently.

 

Tonight's, I installed the Lightroom's iPad app and synced the entire PAX East catalogue. You get an interface that's more relevant to a multitouch device than to a desktop computer. And yet it seems as though you can still express most of your intentions for a photo. Lightroom syncs your edits into the cloud and the cloud syncs into the desktop library.

 

Not bad.

 

Trying out the iOS app was Experiment #1. Oh, and thanks to iOS 8's extensibility features, the presence of the official Flickr app on my iPad meant I could share it directly into my photo stream without any trouble.

 

Experiment #2 was this rather extreme preset Lightroom effect. I was just messing around and pushing buttons and this is what happened. You can probably tell that the lighting in this shot was extreme to begin with. That's why I took the photo to begin with. I zoomed wayyy in and prayed that this woman wouldn't step out of the colored spotlight until I got my camera dialed in just right.

 

I tend to be conservative with my color and lighting adjustments. Every time I push things too far, I back off or hit command-Z. That's limiting, though. I wish I had an eye for the extreme. This particular treatment is way more interesting than the adjustments I'd made by hand.

" - but they are the exception. For this is Balex - the new, tougher, shipping container. Its made by West Virginia from a recently-developed, extra-heavy Culpak extensible paper, the paper that 'gives' under impact where conventional Kraft bursts."

SEC 280 Final Exam

  

Purchase here

  

chosecourses.com/index.php?route=product/category&pat...

  

Product Description

  

Product Description

SEC 280 Final Exam

(TCO 2) What is XKMS?

Key Management Specification, which defines services to manage PKI operations within the Extensible Markup Language (XML) environment

An XML standard for e-mail encryption

An XML standard that is used for wireless data exchange

A primary XML standard that is for application development

(TCO 2) All of the following are techniques used by a social engineer EXCEPT for which one?

An attacker replaces a blank deposit slip in a bank lobby with one containing his own account number

An attacker calls up the IT department posing as an employee and requests a password reset

An attacker runs a brute-force attack on a password

An attacker sends a forged e-mail with a link to a bogus website that has been set to obtain personal information

(TCO 2) Attackers need a certain amount of information before launching their attack. One common place to find information is to go through the trash of the target to find information that could be useful to the attacker. This process of going through a target’s trash is known in the community as _____

Trash rummaging

Garbage surfing

Piggy diving

Dumpster diving

(TCO 2) What are the SSL and TLS used for?

A means of securing application programs on the system

To secure communication over the Internet

A method to change from one form of PKI infrastructure to another

A secure way to reduce the amount of SPAM a system receives

(TCO 2) What are the security risks of installing games on an organization’s system?

There are no significant risks

Users can’t always be sure where the software came from and it may have hidden software inside of it.

The users may play during work hours instead of during breaks

The games may take up too much memory on the computer and slow down processing, making it difficult to work

(TCO 2) What is the ISO 17799?

A standard for creating and implementing security policies

A standard for international encryption of e-mail

A document used to develop physical security for a building

A document describing the details of wireless encryption

(TCO 3) A(n) _____ is a network typically smaller in terms of size and geographic coverage, and consists of two or more connected devices. Home or office networks are typically classified as this type of network

Local-area network

Office-area network

Wide-area network

(TCO 3) What is the main difference between TCP and UDP packets?

UDP packets are a more widely used protocol

TCP packets are smaller and thus more efficient to use

TCP packets are connection oriented, whereas UPD packets are connectionless

UDP is considered to be more reliable because it performs error checking

Internal-area network

(TCO 3) Unfortunately, hackers abuse the ICMP protocol by using it to _____.

Send Internet worms

Launch denial-of-service (DoS) attacks

Steal passwords and credit card numbers

Send spam

(TCO 3) Which transport layer protocol is connectionless?

UDP

TCP

IP

ICMP

(TCO 3) Which of the following is a benefit provided by Network Address Translation (NAT)?

Compensates for the lack of IP addresses

Allows devices using two different protocols to communicate

Creates a DMZ

Translates MAC addresses to IP addresses

(TCO 3) Which transport layer protocol is connection oriented?

UDP

RCP

IS

ICMP

(TCO 3) Which of the following is an example of a MAC address?

00:07:H9:c8:ff:00

00:39:c8:ff:00

00:07:e9:c8:ff:00

00:07:59:c8:ff:00:e8

(TCO 4) All of the following statements sum up the characteristics and requirements of proper private key use EXCEPT which one?

The key should be stored securely

The key should be shared only with others whom you trust

Authentication should be required before the key can be used

The key should be transported securely

(TCO 4) It is easier to implement, back up, and recover keys in a _____.

Centralized infrastructure

Decentralized infrastructure

Hybrid infrastructure

Peer-to-peer infrastructure

(TCO 4) When a message sent by a user is digitally signed with a private key, the person will not be able to deny sending the message. This application of encryption is an example of _____.

Authentication

Nonrepudiation

Confidentiality

Auditing

(TCO 4) Outsourced CAs are different from public CAs in what way?

Outsourced services can be used by hundreds of companies

Outsourced services provide dedicated services and equipment to individual companies

Outsourced services do not maintain specific servers and infrastructures for individual companies

Outsourced services are different in name only. They are essentially the same thing

(TCO 4) Cryptographic algorithms are used for all of the following EXCEPT _____.

Confidentiality

Integrity

Availability

Authentication

(TCO 6) A hub operates at which of the following?

Layer 1, the physical layer

Layer 2, the data-link layer

Layer 2, the MAC layer

Layer 3, the network layer

(TCO 6) Alice sends an e-mail that she encrypts with a shared key, which only she and Bob have. Upon receipt, Bob decrypts the e-mail and reads it. This application of encryption is an example of _____.

Confidentiality

Integrity

Authentication

Nonrepudiation

(TCO 6) The following are steps in securing a workstation EXCEPT _____.

Install NetBIOS and IPX

Install antivirus

Remove unnecessary software

Disable unnecessary user accounts

(TCO 8) Which of the following is a characteristic of the Patriot Act?

Extends the tap-and-trace provisions of existing wiretap statutes to the Internet, and mandates certain technological modifications at ISPs to facilitate electronic wiretaps on the Internet

A major piece of legislation affecting the financial industry, and also one with significant privacy provisions for individuals

Makes it a violation of federal law to knowingly use another’s identity

Implements the principle that a signature, contract, or other record may not be deleted

Denies legal effect, validity, or enforceability solely because it is electronic form

(TCO 8) The Wassenaar Arrangement can be described as which of the following?

An international arrangement on export controls for conventional arms as well as dual-use goods and technologies

An international arrangement on import controls

A rule governing import of encryption in the United States

A rule governing export of encryption in the United States

(TCO 8) What is the Convention on Cybercrime?

A convention of black hats who trade hacking secrets

The first international treaty on crimes committed via the Internet and other computer networks

A convention of white hats who trade hacker prevention knowledge

A treaty regulating international conventions

(TCO 8) The electronic signatures in the Global and National Commerce Act _____.

Implement the principle that a signature, contract, or other record may not be denied legal effect, validity, or enforceability solely because it is electronic form

Address a myriad of legal privacy issues resulting from the increased use of computers and other technology specific to telecommunications

Make it a violation of federal law to knowingly use another’s identity

Are a major piece of legislation affecting the financial industry, and contains significant privacy provisions for individuals

(TCO 2) Give an example of a hoax and how it might actually be destructive

(TCO 2) What are the various ways a backup can be conducted and stored?

Backups should include the organization’s critical data, and…

(TCO 2) List at least five types of disasters that can damage or destroy the information of an organization

(TCO 2) List the four ways backups are conducted and stored.

Full back up, differential backup,…

(TCO 2) List at least five types of disasters that can damage or destroy the information of an organization.

Flood, chemical spill…

(TCO 2) Your boss wants you to give him some suggestions for a policy stating what the individual user responsibilities for information security should be. Create a bulleted list of those responsibilities.

Do not divulge sensitive information to individuals…

(TCO 3) What is the difference between TCP and UDP?

UDP is known as a connectionless protocol, as it has very few…

(TCO 3) List three kinds of information contained in an IP packet header

A unique identifier, distinguishing this packet from other packets…

(TCO 4) What are the laws that govern encryption and digital rights management?

Encryption technology is used to protect digital…

(TCO 5) Describe the laws that govern digital signatures

Digital signatures have the same…

(TCO 6) What are some of the security issues associated with web applications and plug-ins?

Web browsers have mechanisms to enable…

(TCO 6) What are the four common methods for connecting equipment at the physical layer?

Coaxial cable, twisted-pair…

(TCO 6) Describe the functioning of the SSL/TLS suite

SSL and TLS use a combination of symmetric and…

(TCO 6) Explain a simple way to combat boot disks

Disable them or… them in the…

(TCO 7) What are some ethical issues associated with information security?

Ethics is the social-moral environment in which a person makes…

(TCO 9) What are password and domain password policies?

Password complexity policies are designed to deter brute force attacks by increasing the number of possible passwords…

 

En general els adaptadors a format 120 tenen unes proporcions de 6x9 cm, o potser 6x6, però aquest és de 6x8, pel que surt completament de les indicacions que apareixen a la finestreta i un anterior usuari hi va detallar (en aleman) quines xifres corresponen a cada foto. Molt util, em va estalviar la feina a mi. I funciona!

 

La Plaubel Makina II és una càmara de gran format de meitat del s. XX, extensible i destinada sobretot a la premsa. Feia servir plaques de 6,5x9cm però s'adapta sense problemes a porta-rodets de format 120, com en el cas d'aquesta.

 

Les primeres Makina no tenien telèmetre, però a partir de la Makina II del 1933 ja incorpora un. Posteriorment es refinarà el model amb la Makina IIS, que facilita molt el canvi de lents, i ja després de la guerra mundial, l'ultim model és la Makina III, amb molts canvis sobretot per a disparar flaix.

 

De fet, aquesta que tinc és una mica inusual ja que no sembla pas una Makina IIS per tal i com està montada la lent. De fet té dues parts, amb el obturador al mig, el que fa més dificil desmontar-la. Però en canvi té les dues finestretes del telèmetre rectangulars, el que és un element distintiu de les IIS. Probablement sigui una II a la que es va reformar el telèmetre per alguna raó, o bé es tracti d'un model just de transició. El que si no milloraren fou una refotuda manera d'agafar-la. Ergonomía? no en tenien ni idea!!

 

En tot cas és clàrament anterior a la guerra (ja que està marcada amb el DRP "Deutsches Reich Patent" en comptes del DBP de postguerra, "Deutsches BundesPatent". Crec que fou fabricada entre el 1933 i el 1936, més aviat cap al final del periode, ja que el frontal és cromat, i inicialment es produia en negre. Potser fou una de les darreres Makina II (abans del canvi al model IIS) i per això 1936 sembla la data més probable de producció.

 

==================

 

This Plaubel 120 format back is a bit unusual as it gives 6x8 images, so the numbering on the roll does not match. A former owner listed in paper all the changes in the sequence so it could be used. And it works!!

 

The Plaubel Makina II is a large format press camera from the 30's to 50's, strut-folding. It used 6.5x9cm glass plates but also 120 format backs, as this one.

 

The first Makina had no rangefinder, but in 1933 the Makina II already incorporates one. Later, the model will be refined with the Makina II S, which greatly facilitates the change of lens, and even after the World War, the latest model is the Makina III, with many refinements, especially for flash synchro. What they didn't get at all was an easy way to hold it. Ergonomics, what's that??

 

In fact, this one that I have is a little unusual since it does not look like a Makina IIS as the lens has two parts, with the shutter in the middle, which makes it more difficult to disassemble it. But otherwise it has rangefinder rectangular windows, which is a distinctive element of the IIS. It is probably a II to which the rangefinder was reformed for some reason, or it was just a transition model.

 

In any case, it was clearly made before WW2 (since it is marked with the DRP "Deutsches Reich Patent" instead of the post-war DBP, "Deutsches BundesPatent.") I think it was manufactured between 1933 and 1936, rather towards the end of this period, since the front is chromed, and initially it was produced in black. Perhaps it was one of the last Makina II (before the change to the IIS model) and for that reason 1936 seems the most probable date of production.

 

lommen9.home.xs4all.nl/plaubel/index.html

 

www.earlyphotography.co.uk/site/entry_C25.html

 

camera-wiki.org/wiki/Plaubel_Makina#The_6.5.C3.979_rangef...

 

Crawler crane built in minifig scale. Extensible chassis and pneumatically raised boom.

For more pictures visit my MOCPages page.

See also how it works on YouTube.

Mr. Woody takes a peanut snack. according to Moody, the Tsa-La-Gi (Cherokee) people called this bird da-la-la. he was a symbol of war, presumably due to the "scalped" appearance of his brilliant red crown, and the fact they're highly aggressive and nearly fearless (nobody really wants to pick a fight with a guy that's mostly muscle and makes his living pounding on trees with an extension of his head.) Red-bellied woodpeckers are among the few North American species still expanding their range, both to the north and west.

notice his tail against the railing. woodpecker's central tail feathers are specially adapted to allow them to use the tail to help anchor themselves (similar to a tripod with the tail and their feet) on tree trunks/branches as they pound away looking for insects and insect larva. they also have long, extensible tongues to probe for and capture insects. the long tongue "reels up" back and upward into the skull. hummingbirds possess a similar adaptation. ;)

 

(image made thru 2 panes of glass.)

This small fish grows up to 22 cm (8.7 in) long. Like other members of its family, it has a rounded, extensible body, and its soft skin is covered with irregularly-arranged dermal spinules resembling hairs. Its large mouth is forwardly extensible, allowing it to swallow prey as large as itself. The coloring of its body is extremely variable because individual fish tend to match their living environments. Frogfishes have the capacity to change coloration and pigment pattern, taking only a few weeks to adapt. The dominant coloration varies from yellow to brownish-orange, passing through a range of shades, but it can also be green, gray, brown, almost white, or even completely black without any pattern. Body and fins can be marked with roughly parallel dark stripes or elongated blotches, some with rays radiating outward from the eye.

Woodpeckers (Picidae) are a diverse family of birds known for their unique adaptations and behaviors. With over 200 species distributed worldwide, woodpeckers have a rich evolutionary history that spans millions of years. In this brief overview, we will explore the key aspects of woodpecker evolution and their fascinating journey through time.

 

Woodpeckers belong to the order Piciformes, which also includes toucans, barbets, and honeyguides. Their evolutionary origins can be traced back to the early Eocene period, approximately 55 million years ago. Fossil records indicate that the earliest woodpeckers shared similarities with modern forms, possessing a sturdy beak and zygodactyl feet (two toes pointing forward and two backward) that allowed them to cling to trees and excavate cavities.

 

The ancestral woodpeckers likely inhabited forests and woodlands, where they foraged for insects, larvae, and other invertebrates found beneath the bark or within dead wood. Their specialized beak, reinforced with hard keratin and a chisel-like tip, enabled them to drill into tree trunks and extract prey. This feeding strategy provided a selective advantage, driving the diversification and adaptive radiation of woodpeckers into various ecological niches.

 

Over time, woodpeckers underwent further evolutionary adaptations. One of their most remarkable features is the presence of a hyoid apparatus, a complex arrangement of bones and muscles that supports the tongue. The long, extensible tongue can be extended well beyond the bill, allowing woodpeckers to reach deep into crevices and extract hidden prey. This tongue mechanism is unique among birds and contributes to their success as specialized insectivores.

 

Another notable adaptation is the protective features that enable woodpeckers to withstand the repetitive impacts of drumming and excavating. Their brain is encased in a thick, sponge-like skull that acts as a shock absorber, reducing the risk of brain injury. Furthermore, their strong neck muscles and specialized arrangement of bones and cartilage in the skull help distribute the forces generated during pecking, minimizing the strain on their brain and neck.

 

Woodpecker evolution has also led to remarkable diversity in terms of size, coloration, and behavior. Some species, like the great spotted woodpecker (Dendrocopos major), exhibit striking black-and-white plumage with red patches, while others, such as the pileated woodpecker (Dryocopus pileatus), have predominantly black feathers with a vibrant crest. These variations serve various functions, including communication, mate attraction, and camouflage.

 

Woodpeckers are known for their distinct drumming and vocalizations, which play a crucial role in communication and territorial defense. Drumming, achieved by rapid pecking on resonant surfaces like dead wood or metal, serves to establish their presence and ward off potential rivals. Additionally, woodpeckers produce a variety of calls, ranging from rhythmic drum rolls to chirps and rattles, allowing them to communicate with conspecifics across their habitat.

 

The evolutionary success of woodpeckers is evident in their global distribution, with species inhabiting diverse habitats such as forests, woodlands, savannas, and even deserts. They have adapted to various environmental conditions, exploiting niches that offer abundant food resources and suitable nesting sites.

 

In summary, woodpeckers have a long and fascinating evolutionary history that has shaped their unique adaptations and behaviors. From their early origins as insectivorous tree-dwellers to their diverse forms found across the globe today, woodpeckers are a testament to the incredible adaptability and resilience of life. Studying these remarkable birds provides valuable insights into the intricate relationship between form, function, and the ecological roles they play in their respective habitats.

Antennarius pictus @ Seraya's Secret, Tulamben (Bali), Indonesia

 

The painted frogfish or spotted frogfish, Antennarius pictus, is a marine fish belonging to the family Antennariidae.

The painted frogfish grows up to 30 cm (12 in) long. It has a globulous, extensible body, with soft skin is covered with small dermal spinules. Its skin is covered partially with few, small, wart-like protuberances, some variably shaped, scab-like blotches and many small eye spots (ocelli) which look like sponges holes. Its large prognathous mouth allows it to consume prey its same size.

The coloring of the body is extremely variable because they always tend to match their living environments. Frogfishes have the capacity to change coloration and pigment pattern in few weeks. However, the dominant coloration goes from white to black, passing through a whole range of related nuances such as cream, pink, yellow, red, and brown, usually with circular eye spots darker than the background color and/or with saddles and blotches.

Antennarius pictus lives in the tropical and subtropical waters from the Indo-Pacific area, Red Sea included. It is found on sheltered rocky and coral reefs, and adults are usually associated with sponges down to 75 m (246 ft) deep, with an average occurrence at 15 m (49 ft).

As all frogfishes, A. pictus is a voracious carnivore which can attack all small animals that pass within its "strike range", mainly fishes, but even sometimes congeners. Its prey can be close to its own size.

Like other members of its family, the painted frogfish has a benthic and solitary lifestyle. They gather during mating period, but do not tolerate each other any more after the act of fertilization. The male can kill or eat the female if she stays too close [Wikipedia EN].

Crawler crane built in minifig scale. Extensible chassis and pneumatically raised boom.

For more pictures visit my MOCPages page.

See also how it works on YouTube.

Jellyfish, also known sea jellies, are the medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria.

 

Jellyfish are mainly free-swimming marine animals with umbrella-shaped bells and trailing tentacles, although a few are anchored to the seabed by stalks rather than being mobile. The bell can pulsate to provide propulsion for highly efficient locomotion. The tentacles are armed with stinging cells and may be used to capture prey and defend against predators. Jellyfish have a complex life cycle. The medusa is normally the sexual phase, which produces planula larvae; these then disperse widely and enter a sedentary polyp phase, before reaching sexual maturity.

 

Jellyfish are found all over the world, from surface waters to the deep sea. Scyphozoans (the "true jellyfish") are exclusively marine, but some hydrozoans with a similar appearance live in freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide. The medusae of most species are fast-growing, and mature within a few months then die soon after breeding, but the polyp stage, attached to the seabed, may be much more long-lived. Jellyfish have been in existence for at least 500 million years,[1] and possibly 700 million years or more, making them the oldest multi-organ animal group.[2]

 

Jellyfish are eaten by humans in certain cultures. They are considered a delicacy in some Asian countries, where species in the Rhizostomeae order are pressed and salted to remove excess water. Australian researchers have described them as a "perfect food": sustainable and protein-rich but relatively low in food energy.[3]

 

They are also used in research, where the green fluorescent protein used by some species to cause bioluminescence has been adapted as a fluorescent marker for genes inserted into other cells or organisms.

 

The stinging cells used by jellyfish to subdue their prey can injure humans. Thousands of swimmers worldwide are stung every year, with effects ranging from mild discomfort to serious injury or even death. When conditions are favourable, jellyfish can form vast swarms, which can be responsible for damage to fishing gear by filling fishing nets, and sometimes clog the cooling systems of power and desalination plants which draw their water from the sea.

  

Names

The name jellyfish, in use since 1796,[4] has traditionally been applied to medusae and all similar animals including the comb jellies (ctenophores, another phylum).[5][6] The term jellies or sea jellies is more recent, having been introduced by public aquaria in an effort to avoid use of the word "fish" with its modern connotation of an animal with a backbone, though shellfish, cuttlefish and starfish are not vertebrates either.[7][8] In scientific literature, "jelly" and "jellyfish" have been used interchangeably.[9][10] Many sources refer to only scyphozoans as "true jellyfish".[11]

 

A group of jellyfish is called a "smack"[12] or a "smuck".[13]

 

Mapping to taxonomic groups

 

A purple-striped jellyfish at the Monterey Bay Aquarium

Phylogeny

Definition

The term jellyfish broadly corresponds to medusae,[4] that is, a life-cycle stage in the Medusozoa. The American evolutionary biologist Paulyn Cartwright gives the following general definition:

 

Typically, medusozoan cnidarians have a pelagic, predatory jellyfish stage in their life cycle; staurozoans are the exceptions [as they are stalked].[14]

 

The Merriam-Webster dictionary defines jellyfish as follows:

 

A free-swimming marine coelenterate that is the sexually reproducing form of a hydrozoan or scyphozoan and has a nearly transparent saucer-shaped body and extensible marginal tentacles studded with stinging cells.[15]

 

Given that jellyfish is a common name, its mapping to biological groups is inexact. Some authorities have called the comb jellies[16] and certain salps[16] jellyfish, though other authorities state that neither of these are jellyfish, which they consider should be limited to certain groups within the medusozoa.[17][18]

 

The non-medusozoan clades called jellyfish by some but not all authorities (both agreeing and disagreeing citations are given in each case) are indicated with "???" on the following cladogram of the animal kingdom:

 

Animalia

Porifera

 

Ctenophora (comb jellies)[16] ???[17]

 

Cnidaria (includes jellyfish and other jellies)

 

Bilateria

Protostomia

 

Deuterostomia

Ambulacraria

 

Chordata

Tunicata (includes salps)[16] ???[18]

 

Vertebrata

 

Medusozoan jellyfish

Jellyfish are not a clade, as they include most of the Medusozoa, barring some of the Hydrozoa.[19][20] The medusozoan groups included by authorities are indicated on the following phylogenetic tree by the presence of citations. Names of included jellyfish, in English where possible, are shown in boldface; the presence of a named and cited example indicates that at least that species within its group has been called a jellyfish.

 

Cnidaria

Anthozoa (corals)

 

Polypodiozoa and Myxozoa (parasitic cnidarians)

 

Medusozoa

Acraspeda

Staurozoa (stalked jellyfish)[21]

 

Rhopaliophora

Cubozoa (box jellyfish)[16]

 

Scyphozoa

Discomedusae[16]

 

Coronatae (crown jellyfish)[22]

 

(true jellyfish[19])

Hydrozoa

Aplanulata

 

Siphonophorae

 

Some Leptothecata[16] e.g. crystal jelly

 

Filifera[16] e.g. red paper lantern jellyfish[23]

 

Trachylinae

Limnomedusae, e.g. flower hat jelly[16]

 

Narcomedusae, e.g. cosmic jellyfish[24]

 

Taxonomy

The subphylum Medusozoa includes all cnidarians with a medusa stage in their life cycle. The basic cycle is egg, planula larva, polyp, medusa, with the medusa being the sexual stage. The polyp stage is sometimes secondarily lost. The subphylum include the major taxa, Scyphozoa (large jellyfish), Cubozoa (box jellyfish) and Hydrozoa (small jellyfish), and excludes Anthozoa (corals and sea anemones).[25] This suggests that the medusa form evolved after the polyps.[26] Medusozoans have tetramerous symmetry, with parts in fours or multiples of four.[25]

 

The four major classes of medusozoan Cnidaria are:

 

Scyphozoa are sometimes called true jellyfish, though they are no more truly jellyfish than the others listed here. They have tetra-radial symmetry. Most have tentacles around the outer margin of the bowl-shaped bell, and long, oral arms around the mouth in the center of the subumbrella.[25]

Cubozoa (box jellyfish) have a (rounded) box-shaped bell, and their velarium assists them to swim more quickly. Box jellyfish may be related more closely to scyphozoan jellyfish than either are to the Hydrozoa.[26]

Hydrozoa medusae also have tetra-radial symmetry, nearly always have a velum (diaphragm used in swimming) attached just inside the bell margin, do not have oral arms, but a much smaller central stalk-like structure, the manubrium, with terminal mouth opening, and are distinguished by the absence of cells in the mesoglea. Hydrozoa show great diversity of lifestyle; some species maintain the polyp form for their entire life and do not form medusae at all (such as Hydra, which is hence not considered a jellyfish), and a few are entirely medusal and have no polyp form.[25]

Staurozoa (stalked jellyfish) are characterized by a medusa form that is generally sessile, oriented upside down and with a stalk emerging from the apex of the "calyx" (bell), which attaches to the substrate. At least some Staurozoa also have a polyp form that alternates with the medusoid portion of the life cycle. Until recently, Staurozoa were classified within the Scyphozoa.[25]

There are over 200 species of Scyphozoa, about 50 species of Staurozoa, about 50 species of Cubozoa, and the Hydrozoa includes about 1000–1500 species that produce medusae, but many more species that do not.[27][28]

 

Fossil history

 

Fossil jellyfish, Rhizostomites lithographicus, one of the Scypho-medusae, from the Kimmeridgian (late Jurassic, 157 to 152 mya) of Solnhofen, Germany

 

Stranded scyphozoans on a Cambrian tidal flat at Blackberry Hill, Wisconsin

 

The conulariid Conularia milwaukeensis from the Middle Devonian of Wisconsin

Since jellyfish have no hard parts, fossils are rare. The oldest unambiguous fossil of a free-swimming medusa is Burgessomedusa from the mid Cambrian Burgess Shale of Canada, which is likely either a stem group of box jellyfish (Cubozoa) or Acraspeda (the clade including Staurozoa, Cubozoa, and Scyphozoa). Other claimed records from the Cambrian of China and Utah in the United States are uncertain, and possibly represent ctenophores instead.[29]

 

Anatomy

 

Labelled cross section of a jellyfish

The main feature of a true jellyfish is the umbrella-shaped bell. This is a hollow structure consisting of a mass of transparent jelly-like matter known as mesoglea, which forms the hydrostatic skeleton of the animal.[25] 95% or more of the mesogloea consists of water,[30] but it also contains collagen and other fibrous proteins, as well as wandering amoebocytes which can engulf debris and bacteria. The mesogloea is bordered by the epidermis on the outside and the gastrodermis on the inside. The edge of the bell is often divided into rounded lobes known as lappets, which allow the bell to flex. In the gaps or niches between the lappets are dangling rudimentary sense organs known as rhopalia, and the margin of the bell often bears tentacles.[25]

  

Anatomy of a scyphozoan jellyfish

On the underside of the bell is the manubrium, a stalk-like structure hanging down from the centre, with the mouth, which also functions as the anus, at its tip. There are often four oral arms connected to the manubrium, streaming away into the water below.[31] The mouth opens into the gastrovascular cavity, where digestion takes place and nutrients are absorbed. This is subdivided by four thick septa into a central stomach and four gastric pockets. The four pairs of gonads are attached to the septa, and close to them four septal funnels open to the exterior, perhaps supplying good oxygenation to the gonads. Near the free edges of the septa, gastric filaments extend into the gastric cavity; these are armed with nematocysts and enzyme-producing cells and play a role in subduing and digesting the prey. In some scyphozoans, the gastric cavity is joined to radial canals which branch extensively and may join a marginal ring canal. Cilia in these canals circulate the fluid in a regular direction.[25]

  

Discharge mechanism of a nematocyst

The box jellyfish is largely similar in structure. It has a squarish, box-like bell. A short pedalium or stalk hangs from each of the four lower corners. One or more long, slender tentacles are attached to each pedalium.[32] The rim of the bell is folded inwards to form a shelf known as a velarium which restricts the bell's aperture and creates a powerful jet when the bell pulsates, allowing box jellyfish to swim faster than true jellyfish.[25] Hydrozoans are also similar, usually with just four tentacles at the edge of the bell, although many hydrozoans are colonial and may not have a free-living medusal stage. In some species, a non-detachable bud known as a gonophore is formed that contains a gonad but is missing many other medusal features such as tentacles and rhopalia.[25] Stalked jellyfish are attached to a solid surface by a basal disk, and resemble a polyp, the oral end of which has partially developed into a medusa with tentacle-bearing lobes and a central manubrium with four-sided mouth.[25]

 

Most jellyfish do not have specialized systems for osmoregulation, respiration and circulation, and do not have a central nervous system. Nematocysts, which deliver the sting, are located mostly on the tentacles; true jellyfish also have them around the mouth and stomach.[33] Jellyfish do not need a respiratory system because sufficient oxygen diffuses through the epidermis. They have limited control over their movement, but can navigate with the pulsations of the bell-like body; some species are active swimmers most of the time, while others largely drift.[34] The rhopalia contain rudimentary sense organs which are able to detect light, water-borne vibrations, odour and orientation.[25] A loose network of nerves called a "nerve net" is located in the epidermis.[35][36] Although traditionally thought not to have a central nervous system, nerve net concentration and ganglion-like structures could be considered to constitute one in most species.[37] A jellyfish detects stimuli, and transmits impulses both throughout the nerve net and around a circular nerve ring, to other nerve cells. The rhopalial ganglia contain pacemaker neurones which control swimming rate and direction.[25]

 

In many species of jellyfish, the rhopalia include ocelli, light-sensitive organs able to tell light from dark. These are generally pigment spot ocelli, which have some of their cells pigmented. The rhopalia are suspended on stalks with heavy crystals at one end, acting like gyroscopes to orient the eyes skyward. Certain jellyfish look upward at the mangrove canopy while making a daily migration from mangrove swamps into the open lagoon, where they feed, and back again.[2]

 

Box jellyfish have more advanced vision than the other groups. Each individual has 24 eyes, two of which are capable of seeing colour, and four parallel information processing areas that act in competition,[38] supposedly making them one of the few kinds of animal to have a 360-degree view of its environment.[39]

 

Box jellyfish eye

The study of jellyfish eye evolution is an intermediary to a better understanding of how visual systems evolved on Earth.[40] Jellyfish exhibit immense variation in visual systems ranging from photoreceptive cell patches seen in simple photoreceptive systems to more derived complex eyes seen in box jellyfish.[40] Major topics of jellyfish visual system research (with an emphasis on box jellyfish) include: the evolution of jellyfish vision from simple to complex visual systems), the eye morphology and molecular structures of box jellyfish (including comparisons to vertebrate eyes), and various uses of vision including task-guided behaviors and niche specialization.

 

Evolution

Experimental evidence for photosensitivity and photoreception in cnidarians antecedes the mid 1900s, and a rich body of research has since covered evolution of visual systems in jellyfish.[41] Jellyfish visual systems range from simple photoreceptive cells to complex image-forming eyes. More ancestral visual systems incorporate extraocular vision (vision without eyes) that encompass numerous receptors dedicated to single-function behaviors. More derived visual systems comprise perception that is capable of multiple task-guided behaviors.

 

Although they lack a true brain, cnidarian jellyfish have a "ring" nervous system that plays a significant role in motor and sensory activity. This net of nerves is responsible for muscle contraction and movement and culminates the emergence of photosensitive structures.[40] Across Cnidaria, there is large variation in the systems that underlie photosensitivity. Photosensitive structures range from non-specialized groups of cells, to more "conventional" eyes similar to those of vertebrates.[41] The general evolutionary steps to develop complex vision include (from more ancestral to more derived states): non-directional photoreception, directional photoreception, low-resolution vision, and high-resolution vision.[40] Increased habitat and task complexity has favored the high-resolution visual systems common in derived cnidarians such as box jellyfish.[40]

 

Basal visual systems observed in various cnidarians exhibit photosensitivity representative of a single task or behavior. Extraocular photoreception (a form of non-directional photoreception), is the most basic form of light sensitivity and guides a variety of behaviors among cnidarians. It can function to regulate circadian rhythm (as seen in eyeless hydrozoans) and other light-guided behaviors responsive to the intensity and spectrum of light. Extraocular photoreception can function additionally in positive phototaxis (in planula larvae of hydrozoans),[41] as well as in avoiding harmful amounts of UV radiation via negative phototaxis. Directional photoreception (the ability to perceive direction of incoming light) allows for more complex phototactic responses to light, and likely evolved by means of membrane stacking.[40] The resulting behavioral responses can range from guided spawning events timed by moonlight to shadow responses for potential predator avoidance.[41][42] Light-guided behaviors are observed in numerous scyphozoans including the common moon jelly, Aurelia aurita, which migrates in response to changes in ambient light and solar position even though they lack proper eyes.[41]

 

The low-resolution visual system of box jellyfish is more derived than directional photoreception, and thus box jellyfish vision represents the most basic form of true vision in which multiple directional photoreceptors combine to create the first imaging and spatial resolution. This is different from the high-resolution vision that is observed in camera or compound eyes of vertebrates and cephalopods that rely on focusing optics.[41] Critically, the visual systems of box jellyfish are responsible for guiding multiple tasks or behaviors in contrast to less derived visual systems in other jellyfish that guide single behavioral functions. These behaviors include phototaxis based on sunlight (positive) or shadows (negative), obstacle avoidance, and control of swim-pulse rate.[43]

 

Box jellyfish possess "proper eyes" (similar to vertebrates) that allow them to inhabit environments that lesser derived medusae cannot. In fact, they are considered the only class in the clade Medusozoa that have behaviors necessitating spatial resolution and genuine vision.[41] However, the lens in their eyes are more functionally similar to cup-eyes exhibited in low-resolution organisms, and have very little to no focusing capability.[44][43] The lack of the ability to focus is due to the focal length exceeding the distance to the retina, thus generating unfocused images and limiting spatial resolution.[41] The visual system is still sufficient for box jellyfish to produce an image to help with tasks such as object avoidance.

 

Utility as a model organism

Box jellyfish eyes are a visual system that is sophisticated in numerous ways. These intricacies include the considerable variation within the morphology of box jellyfishes' eyes (including their task/behavior specification), and the molecular makeup of their eyes including: photoreceptors, opsins, lenses, and synapses.[41] The comparison of these attributes to more derived visual systems can allow for a further understanding of how the evolution of more derived visual systems may have occurred, and puts into perspective how box jellyfish can play the role as an evolutionary/developmental model for all visual systems.[45]

 

Characteristics

Box jellyfish visual systems are both diverse and complex, comprising multiple photosystems.[41] There is likely considerable variation in visual properties between species of box jellyfish given the significant inter-species morphological and physiological variation. Eyes tend to differ in size and shape, along with number of receptors (including opsins), and physiology across species of box jellyfish.[41]

 

Box jellyfish have a series of intricate lensed eyes that are similar to those of more derived multicellular organisms such as vertebrates. Their 24 eyes fit into four different morphological categories.[46] These categories consist of two large, morphologically different medial eyes (a lower and upper lensed eye) containing spherical lenses, a lateral pair of pigment slit eyes, and a lateral pair of pigment pit eyes.[43] The eyes are situated on rhopalia (small sensory structures) which serve sensory functions of the box jellyfish and arise from the cavities of the exumbrella (the surface of the body) on the side of the bells of the jellyfish.[41] The two large eyes are located on the mid-line of the club and are considered complex because they contain lenses. The four remaining eyes lie laterally on either side of each rhopalia and are considered simple. The simple eyes are observed as small invaginated cups of epithelium that have developed pigmentation.[47] The larger of the complex eyes contains a cellular cornea created by a mono ciliated epithelium, cellular lens, homogenous capsule to the lens, vitreous body with prismatic elements, and a retina of pigmented cells. The smaller of the complex eyes is said to be slightly less complex given that it lacks a capsule but otherwise contains the same structure as the larger eye.[47]

 

Box jellyfish have multiple photosystems that comprise different sets of eyes.[41] Evidence includes immunocytochemical and molecular data that show photopigment differences among the different morphological eye types, and physiological experiments done on box jellyfish to suggest behavioral differences among photosystems. Each individual eye type constitutes photosystems that work collectively to control visually guided behaviors.[41]

 

Box jellyfish eyes primarily use c-PRCs (ciliary photoreceptor cells) similar to that of vertebrate eyes. These cells undergo phototransduction cascades (process of light absorption by photoreceptors) that are triggered by c-opsins.[48] Available opsin sequences suggest that there are two types of opsins possessed by all cnidarians including an ancient phylogenetic opsin, and a sister ciliary opsin to the c-opsins group. Box jellyfish could have both ciliary and cnidops (cnidarian opsins), which is something not previously believed to appear in the same retina.[41] Nevertheless, it is not entirely evident whether cnidarians possess multiple opsins that are capable of having distinctive spectral sensitivities.[41]

 

Comparison with other organisms

Comparative research on genetic and molecular makeup of box jellyfishes' eyes versus more derived eyes seen in vertebrates and cephalopods focuses on: lenses and crystallin composition, synapses, and Pax genes and their implied evidence for shared primordial (ancestral) genes in eye evolution.[49]

 

Box jellyfish eyes are said to be an evolutionary/developmental model of all eyes based on their evolutionary recruitment of crystallins and Pax genes.[45] Research done on box jellyfish including Tripedalia cystophora has suggested that they possess a single Pax gene, PaxB. PaxB functions by binding to crystallin promoters and activating them. PaxB in situ hybridization resulted in PaxB expression in the lens, retina, and statocysts.[45] These results and the rejection of the prior hypothesis that Pax6 was an ancestral Pax gene in eyes has led to the conclusion that PaxB was a primordial gene in eye evolution, and that the eyes of all organisms likely share a common ancestor.[45]

 

The lens structure of box jellyfish appears very similar to those of other organisms, but the crystallins are distinct in both function and appearance.[49] Weak reactions were seen within the sera and there were very weak sequence similarities within the crystallins among vertebrate and invertebrate lenses.[49] This is likely due to differences in lower molecular weight proteins and the subsequent lack of immunological reactions with antisera that other organisms' lenses exhibit.[49]

 

All four of the visual systems of box jellyfish species investigated with detail (Carybdea marsupialis, Chiropsalmus quadrumanus, Tamoya haplonema and Tripedalia cystophora) have invaginated synapses, but only in the upper and lower lensed eyes. Different densities were found between the upper and lower lenses, and between species.[46] Four types of chemical synapses have been discovered within the rhopalia which could help in understanding neural organization including: clear unidirectional, dense-core unidirectional, clear bidirectional, and clear and dense-core bidirectional. The synapses of the lensed eyes could be useful as markers to learn more about the neural circuit in box jellyfish retinal areas.[46]

 

Evolution as a response to natural stimuli

The primary adaptive responses to environmental variation observed in box jellyfish eyes include pupillary constriction speeds in response to light environments, as well as photoreceptor tuning and lens adaptations to better respond to shifts between light environments and darkness. Interestingly, some box jellyfish species' eyes appear to have evolved more focused vision in response to their habitat.[50]

 

Pupillary contraction appears to have evolved in response to variation in the light environment across ecological niches across three species of box jellyfish (Chironex fleckeri, Chiropsella bronzie, and Carukia barnesi). Behavioral studies suggest that faster pupil contraction rates allow for greater object avoidance,[50] and in fact, species with more complex habitats exhibit faster rates. Ch. bronzie inhabit shallow beach fronts that have low visibility and very few obstacles, thus, faster pupil contraction in response to objects in their environment is not important. Ca. barnesi and Ch. fleckeri are found in more three-dimensionally complex environments like mangroves with an abundance of natural obstacles, where faster pupil contraction is more adaptive.[50] Behavioral studies support the idea that faster pupillary contraction rates assist with obstacle avoidance as well as depth adjustments in response to differing light intensities.

 

Light/dark adaptation via pupillary light reflexes is an additional form of an evolutionary response to the light environment. This relates to the pupil's response to shifts between light intensity (generally from sunlight to darkness). In the process of light/dark adaptation, the upper and lower lens eyes of different box jellyfish species vary in specific function.[43] The lower lens-eyes contain pigmented photoreceptors and long pigment cells with dark pigments that migrate on light/dark adaptation, while the upper-lens eyes play a concentrated role in light direction and phototaxis given that they face upward towards the water surface (towards the sun or moon).[43] The upper lens of Ch. bronzie does not exhibit any considerable optical power while Tr. cystophora (a box jellyfish species that tends to live in mangroves) does. The ability to use light to visually guide behavior is not of as much importance to Ch. bronzie as it is to species in more obstacle-filled environments.[43] Differences in visually guided behavior serve as evidence that species that share the same number and structure of eyes can exhibit differences in how they control behavior.

 

Largest and smallest

Jellyfish range from about one millimeter in bell height and diameter,[51] to nearly 2 metres (6+1⁄2 ft) in bell height and diameter; the tentacles and mouth parts usually extend beyond this bell dimension.[25]

 

The smallest jellyfish are the peculiar creeping jellyfish in the genera Staurocladia and Eleutheria, which have bell disks from 0.5 millimetres (1⁄32 in) to a few millimeters in diameter, with short tentacles that extend out beyond this, which these jellyfish use to move across the surface of seaweed or the bottoms of rocky pools;[51] many of these tiny creeping jellyfish cannot be seen in the field without a hand lens or microscope. They can reproduce asexually by fission (splitting in half). Other very small jellyfish, which have bells about one millimeter, are the hydromedusae of many species that have just been released from their parent polyps;[52] some of these live only a few minutes before shedding their gametes in the plankton and then dying, while others will grow in the plankton for weeks or months. The hydromedusae Cladonema radiatum and Cladonema californicum are also very small, living for months, yet never growing beyond a few mm in bell height and diameter.[53]

  

The lion's mane jellyfish (Cyanea capillata) is one of the largest species.

The lion's mane jellyfish, Cyanea capillata, was long-cited as the largest jellyfish, and arguably the longest animal in the world, with fine, thread-like tentacles that may extend up to 36.5 m (119 ft 9 in) long (though most are nowhere near that large).[54][55] They have a moderately painful, but rarely fatal, sting.[56] The increasingly common giant Nomura's jellyfish, Nemopilema nomurai, found in some, but not all years in the waters of Japan, Korea and China in summer and autumn is another candidate for "largest jellyfish", in terms of diameter and weight, since the largest Nomura's jellyfish in late autumn can reach 2 m (6 ft 7 in) in bell (body) diameter and about 200 kg (440 lb) in weight, with average specimens frequently reaching 0.9 m (2 ft 11 in) in bell diameter and about 150 kg (330 lb) in weight.[57][58] The large bell mass of the giant Nomura's jellyfish[59] can dwarf a diver and is nearly always much greater than the Lion's Mane, whose bell diameter can reach 1 m (3 ft 3 in).[60]

 

The rarely encountered deep-sea jellyfish Stygiomedusa gigantea is another candidate for "largest jellyfish", with its thick, massive bell up to 100 cm (3 ft 3 in) wide, and four thick, "strap-like" oral arms extending up to 6 m (19+1⁄2 ft) in length, very different from the typical fine, threadlike tentacles that rim the umbrella of more-typical-looking jellyfish, including the Lion's Mane.[61]

 

Desmonema glaciale, which lives in the Antarctic region, can reach a very large size (several meters).[62][63] Purple-striped jelly (Chrysaora colorata) can also be extremely long (up to 15 feet).[64]

 

Life history and behavior

See also: Biological life cycle and Developmental biology

Illustration of two life stages of seven jelly species

The developmental stages of scyphozoan jellyfish's life cycle:

1–3 Larva searches for site

4–8 Polyp grows

9–11 Polyp strobilates

12–14 Medusa grows

Life cycle

Jellyfish have a complex life cycle which includes both sexual and asexual phases, with the medusa being the sexual stage in most instances. Sperm fertilize eggs, which develop into larval planulae, become polyps, bud into ephyrae and then transform into adult medusae. In some species certain stages may be skipped.[65]

 

Upon reaching adult size, jellyfish spawn regularly if there is a sufficient supply of food. In most species, spawning is controlled by light, with all individuals spawning at about the same time of day; in many instances this is at dawn or dusk.[66] Jellyfish are usually either male or female (with occasional hermaphrodites). In most cases, adults release sperm and eggs into the surrounding water, where the unprotected eggs are fertilized and develop into larvae. In a few species, the sperm swim into the female's mouth, fertilizing the eggs within her body, where they remain during early development stages. In moon jellies, the eggs lodge in pits on the oral arms, which form a temporary brood chamber for the developing planula larvae.[67]

 

The planula is a small larva covered with cilia. When sufficiently developed, it settles onto a firm surface and develops into a polyp. The polyp generally consists of a small stalk topped by a mouth that is ringed by upward-facing tentacles. The polyps resemble those of closely related anthozoans, such as sea anemones and corals. The jellyfish polyp may be sessile, living on the bottom, boat hulls or other substrates, or it may be free-floating or attached to tiny bits of free-living plankton[68] or rarely, fish[69][70] or other invertebrates. Polyps may be solitary or colonial.[71] Most polyps are only millimetres in diameter and feed continuously. The polyp stage may last for years.[25]

 

After an interval and stimulated by seasonal or hormonal changes, the polyp may begin reproducing asexually by budding and, in the Scyphozoa, is called a segmenting polyp, or a scyphistoma. Budding produces more scyphistomae and also ephyrae.[25] Budding sites vary by species; from the tentacle bulbs, the manubrium (above the mouth), or the gonads of hydromedusae.[68] In a process known as strobilation, the polyp's tentacles are reabsorbed and the body starts to narrow, forming transverse constrictions, in several places near the upper extremity of the polyp. These deepen as the constriction sites migrate down the body, and separate segments known as ephyra detach. These are free-swimming precursors of the adult medusa stage, which is the life stage that is typically identified as a jellyfish.[25][72] The ephyrae, usually only a millimeter or two across initially, swim away from the polyp and grow. Limnomedusae polyps can asexually produce a creeping frustule larval form, which crawls away before developing into another polyp.[25] A few species can produce new medusae by budding directly from the medusan stage. Some hydromedusae reproduce by fission.[68]

 

Lifespan

Little is known of the life histories of many jellyfish as the places on the seabed where the benthic forms of those species live have not been found. However, an asexually reproducing strobila form can sometimes live for several years, producing new medusae (ephyra larvae) each year.[73]

 

An unusual species, Turritopsis dohrnii, formerly classified as Turritopsis nutricula,[74] might be effectively immortal because of its ability under certain circumstances to transform from medusa back to the polyp stage, thereby escaping the death that typically awaits medusae post-reproduction if they have not otherwise been eaten by some other organism. So far this reversal has been observed only in the laboratory.[75]

 

Locomotion

 

Jellyfish locomotion is highly efficient. Muscles in the jellylike bell contract, setting up a start vortex and propelling the animal. When the contraction ends, the bell recoils elastically, creating a stop vortex with no extra energy input.

Using the moon jelly Aurelia aurita as an example, jellyfish have been shown to be the most energy-efficient swimmers of all animals.[76] They move through the water by radially expanding and contracting their bell-shaped bodies to push water behind them. They pause between the contraction and expansion phases to create two vortex rings. Muscles are used for the contraction of the body, which creates the first vortex and pushes the animal forward, but the mesoglea is so elastic that the expansion is powered exclusively by relaxing the bell, which releases the energy stored from the contraction. Meanwhile, the second vortex ring starts to spin faster, sucking water into the bell and pushing against the centre of the body, giving a secondary and "free" boost forward. The mechanism, called passive energy recapture, only works in relatively small jellyfish moving at low speeds, allowing the animal to travel 30 percent farther on each swimming cycle. Jellyfish achieved a 48 percent lower cost of transport (food and oxygen intake versus energy spent in movement) than other animals in similar studies. One reason for this is that most of the gelatinous tissue of the bell is inactive, using no energy during swimming.[77]

 

Ecology

Diet

Jellyfish are, like other cnidarians, generally carnivorous (or parasitic),[78] feeding on planktonic organisms, crustaceans, small fish, fish eggs and larvae, and other jellyfish, ingesting food and voiding undigested waste through the mouth. They hunt passively using their tentacles as drift lines, or sink through the water with their tentacles spread widely; the tentacles, which contain nematocysts to stun or kill the prey, may then flex to help bring it to the mouth.[25] Their swimming technique also helps them to capture prey; when their bell expands it sucks in water which brings more potential prey within reach of the tentacles.[79]

 

A few species such as Aglaura hemistoma are omnivorous, feeding on microplankton which is a mixture of zooplankton and phytoplankton (microscopic plants) such as dinoflagellates.[80] Others harbour mutualistic algae (Zooxanthellae) in their tissues;[25] the spotted jellyfish (Mastigias papua) is typical of these, deriving part of its nutrition from the products of photosynthesis, and part from captured zooplankton.[81][82] The upside-down jellyfish (Cassiopea andromeda) also has a symbiotic relationship with microalgae, but captures tiny animals to supplement their diet. This is done by releasing tiny balls of living cells composed of mesoglea. These use cilia to drive them through water and stinging cells which stun the prey. The blobs also seems to have digestive capabilities.[83]

 

Predation

Other species of jellyfish are among the most common and important jellyfish predators. Sea anemones may eat jellyfish that drift into their range. Other predators include tunas, sharks, swordfish, sea turtles and penguins.[84][85] Jellyfish washed up on the beach are consumed by foxes, other terrestrial mammals and birds.[86] In general however, few animals prey on jellyfish; they can broadly be considered to be top predators in the food chain. Once jellyfish have become dominant in an ecosystem, for example through overfishing which removes predators of jellyfish larvae, there may be no obvious way for the previous balance to be restored: they eat fish eggs and juvenile fish, and compete with fish for food, preventing fish stocks from recovering.[87]

 

Symbiosis

Some small fish are immune to the stings of the jellyfish and live among the tentacles, serving as bait in a fish trap; they are safe from potential predators and are able to share the fish caught by the jellyfish.[88] The cannonball jellyfish has a symbiotic relationship with ten different species of fish, and with the longnose spider crab, which lives inside the bell, sharing the jellyfish's food and nibbling its tissues.[89]

 

Blooms

Main article: Jellyfish bloom

 

Map of population trends of native and invasive jellyfish.[90]

Circles represent data records; larger circles denote higher certainty of findings.

Increase (high certainty)

Increase (low certainty)

Stable/variable

Decrease

No data

Jellyfish form large masses or blooms in certain environmental conditions of ocean currents, nutrients, sunshine, temperature, season, prey availability, reduced predation and oxygen concentration. Currents collect jellyfish together, especially in years with unusually high populations. Jellyfish can detect marine currents and swim against the current to congregate in blooms.[91][92] Jellyfish are better able to survive in nutrient-rich, oxygen-poor water than competitors, and thus can feast on plankton without competition. Jellyfish may also benefit from saltier waters, as saltier waters contain more iodine, which is necessary for polyps to turn into jellyfish. Rising sea temperatures caused by climate change may also contribute to jellyfish blooms, because many species of jellyfish are able to survive in warmer waters.[93] Increased nutrients from agricultural or urban runoff with nutrients including nitrogen and phosphorus compounds increase the growth of phytoplankton, causing eutrophication and algal blooms. When the phytoplankton die, they may create dead zones, so-called because they are hypoxic (low in oxygen). This in turn kills fish and other animals, but not jellyfish,[94] allowing them to bloom.[95][96] Jellyfish populations may be expanding globally as a result of land runoff and overfishing of their natural predators.[97][98] Jellyfish are well placed to benefit from disturbance of marine ecosystems. They reproduce rapidly; they prey upon many species, while few species prey on them; and they feed via touch rather than visually, so they can feed effectively at night and in turbid waters.[99][100] It may be difficult for fish stocks to re-establish themselves in marine ecosystems once they have become dominated by jellyfish, because jellyfish feed on plankton, which includes fish eggs and larvae.[101][102][96]

  

Moon jellyfishes can live in northern hemisphere seas,[103][104] such as the Baltic Sea.[105][106]

As suspected at the turn of this century, [107][108] jellyfish blooms are increasing in frequency. Between 2013 and 2020 the Mediterranean Science Commission monitored on a weekly basis the frequency of such outbreaks in coastal waters from Morocco to the Black Sea, revealing a relatively high frequency of these blooms nearly all year round, with peaks observed from March to July and often again in the autumn. The blooms are caused by different jellyfish species, depending on their localisation within the Basin: one observes a clear dominance of Pelagia noctiluca and Velella velella outbreaks in the western Mediterranean, of Rhizostoma pulmo and Rhopilema nomadica outbreaks in the eastern Mediterranean, and of Aurelia aurita and Mnemiopsis leidyi outbreaks in the Black Sea.[109]

 

Some jellyfish populations that have shown clear increases in the past few decades are invasive species, newly arrived from other habitats: examples include the Black Sea, Caspian Sea, Baltic Sea, central and eastern Mediterranean, Hawaii, and tropical and subtropical parts of the West Atlantic (including the Caribbean, Gulf of Mexico and Brazil).[105][106]

 

Jellyfish blooms can have significant impact on community structure. Some carnivorous jellyfish species prey on zooplankton while others graze on primary producers.[110] Reductions in zooplankton and ichthyoplankton due to a jellyfish bloom can ripple through the trophic levels. High-density jellyfish populations can outcompete other predators and reduce fish recruitment.[111] Increased grazing on primary producers by jellyfish can also interrupt energy transfer to higher trophic levels.[112]

 

During blooms, jellyfish significantly alter the nutrient availability in their environment. Blooms require large amounts of available organic nutrients in the water column to grow, limiting availability for other organisms.[113] Some jellyfish have a symbiotic relationship with single-celled dinoflagellates, allowing them to assimilate inorganic carbon, phosphorus, and nitrogen creating competition for phytoplankton.[113] Their large biomass makes them an important source of dissolved and particulate organic matter for microbial communities through excretion, mucus production, and decomposition.[90][114] The microbes break down the organic matter into inorganic ammonium and phosphate. However, the low carbon availability shifts the process from production to respiration creating low oxygen areas making the dissolved inorganic nitrogen and phosphorus largely unavailable for primary production.

 

These blooms have very real impacts on industries. Jellyfish can outcompete fish by utilizing open niches in over-fished fisheries.[115] Catch of jellyfish can strain fishing gear and lead to expenses relating to damaged gear. Power plants have been shut down due to jellyfish blocking the flow of cooling water.[116] Blooms have also been harmful for tourism, causing a rise in stings and sometimes the closure of beaches.[117]

 

Jellyfish form a component of jelly-falls, events where gelatinous zooplankton fall to the seafloor, providing food for the benthic organisms there.[118] In temperate and subpolar regions, jelly-falls usually follow immediately after a bloom.[119]

 

Habitats

 

A common Scyphozoan jellyfish seen near beaches in the Florida Panhandle

Most jellyfish are marine animals, although a few hydromedusae inhabit freshwater. The best known freshwater example is the cosmopolitan hydrozoan jellyfish, Craspedacusta sowerbii. It is less than an inch (2.5 cm) in diameter, colorless and does not sting.[120] Some jellyfish populations have become restricted to coastal saltwater lakes, such as Jellyfish Lake in Palau.[121] Jellyfish Lake is a marine lake where millions of golden jellyfish (Mastigias spp.) migrate horizontally across the lake daily.[82]

 

Although most jellyfish live well off the ocean floor and form part of the plankton, a few species are closely associated with the bottom for much of their lives and can be considered benthic. The upside-down jellyfish in the genus Cassiopea typically lie on the bottom of shallow lagoons where they sometimes pulsate gently with their umbrella top facing down. Even some deep-sea species of hydromedusae and scyphomedusae are usually collected on or near the bottom. All of the stauromedusae are found attached to either seaweed or rocky or other firm material on the bottom.[122]

 

Some species explicitly adapt to tidal flux. In Roscoe Bay, jellyfish ride the current at ebb tide until they hit a gravel bar, and then descend below the current. They remain in still waters until the tide rises, ascending and allowing it to sweep them back into the bay. They also actively avoid fresh water from mountain snowmelt, diving until they find enough salt.

  

Parasites

Jellyfish are hosts to a wide variety of parasitic organisms. They act as intermediate hosts of endoparasitic helminths, with the infection being transferred to the definitive host fish after predation. Some digenean trematodes, especially species in the family Lepocreadiidae, use jellyfish as their second intermediate hosts. Fish become infected by the trematodes when they feed on infected jellyfish.

 

Relation to humans

Jellyfish have long been eaten in some parts of the world. Fisheries have begun harvesting the American cannonball jellyfish, Stomolophus meleagris, along the southern Atlantic coast of the United States and in the Gulf of Mexico for export to Asia.

 

Jellyfish are also harvested for their collagen, which is being investigated for use in a variety of applications including the treatment of rheumatoid arthritis.

 

Aquaculture and fisheries of other species often suffer severe losses – and so losses of productivity – due to jellyfish.

 

Products

Main article: Jellyfish as food

In some countries, including China, Japan, and Korea, jellyfish are a delicacy. The jellyfish is dried to prevent spoiling. Only some 12 species of scyphozoan jellyfish belonging to the order Rhizostomeae are harvested for food, mostly in southeast Asia. Rhizostomes, especially Rhopilema esculentum in China (海蜇 hǎizhé, 'sea stingers') and Stomolophus meleagris (cannonball jellyfish) in the United States, are favored because of their larger and more rigid bodies and because their toxins are harmless to humans.

 

Traditional processing methods, carried out by a jellyfish master, involve a 20- to 40-day multi-phase procedure in which, after removing the gonads and mucous membranes, the umbrella and oral arms are treated with a mixture of table salt and alum, and compressed. Processing makes the jellyfish drier and more acidic, producing a crisp texture. Jellyfish prepared this way retain 7–10% of their original weight, and the processed product consists of approximately 94% water and 6% protein. Freshly processed jellyfish has a white, creamy color and turns yellow or brown during prolonged storage.

 

In China, processed jellyfish are desalted by soaking in water overnight and eaten cooked or raw. The dish is often served shredded with a dressing of oil, soy sauce, vinegar and sugar, or as a salad with vegetables. In Japan, cured jellyfish are rinsed, cut into strips and served with vinegar as an appetizer. Desalted, ready-to-eat products are also available.

 

Biotechnology

The hydromedusa Aequorea victoria was the source of green fluorescent protein, studied for its role in bioluminescence and later for use as a marker in genetic engineering.

Pliny the Elder reported in his Natural History that the slime of the jellyfish "Pulmo marinus" produced light when rubbed on a walking stick.

 

In 1961, Osamu Shimomura extracted green fluorescent protein (GFP) and another bioluminescent protein, called aequorin, from the large and abundant hydromedusa Aequorea victoria, while studying photoproteins that cause bioluminescence in this species. Three decades later, Douglas Prasher sequenced and cloned the gene for GFP. Martin Chalfie figured out how to use GFP as a fluorescent marker of genes inserted into other cells or organisms. Roger Tsien later chemically manipulated GFP to produce other fluorescent colors to use as markers. In 2008, Shimomura, Chalfie and Tsien won the Nobel Prize in Chemistry for their work with GFP. Man-made GFP became widely used as a fluorescent tag to show which cells or tissues express specific genes. The genetic engineering technique fuses the gene of interest to the GFP gene. The fused DNA is then put into a cell, to generate either a cell line or (via IVF techniques) an entire animal bearing the gene. In the cell or animal, the artificial gene turns on in the same tissues and the same time as the normal gene, making a fusion of the normal protein with GFP attached to the end, illuminating the animal or cell reveals what tissues express that protein—or at what stage of development. The fluorescence shows where the gene is expressed.

 

Aquarium display

Jellyfish are displayed in many public aquariums. Often the tank's background is blue and the animals are illuminated by side light, increasing the contrast between the animal and the background. In natural conditions, many jellies are so transparent that they are nearly invisible. Jellyfish are not adapted to closed spaces. They depend on currents to transport them from place to place. Professional exhibits as in the Monterey Bay Aquarium feature precise water flows, typically in circular tanks to avoid trapping specimens in corners. The outflow is spread out over a large surface area and the inflow enters as a sheet of water in front of the outflow, so the jellyfish do not get sucked into it. As of 2009, jellyfish were becoming popular in home aquariums, where they require similar equipment.

 

Stings

Jellyfish are armed with nematocysts, a type of specialized stinging cell. Contact with a jellyfish tentacle can trigger millions of nematocysts to pierce the skin and inject venom, but only some species' venom causes an adverse reaction in humans. In a study published in Communications Biology, researchers found a jellyfish species called Cassiopea xamachana which when triggered will release tiny balls of cells that swim around the jellyfish stinging everything in their path. Researchers described these as "self-propelling microscopic grenades" and named them cassiosomes.

 

The effects of stings range from mild discomfort to extreme pain and death. Most jellyfish stings are not deadly, but stings of some box jellyfish (Irukandji jellyfish), such as the sea wasp, can be deadly. Stings may cause anaphylaxis (a form of shock), which can be fatal. Jellyfish kill 20 to 40 people a year in the Philippines alone. In 2006 the Spanish Red Cross treated 19,000 stung swimmers along the Costa Brava.

 

Vinegar (3–10% aqueous acetic acid) may help with box jellyfish stings but not the stings of the Portuguese man o' war. Clearing the area of jelly and tentacles reduces nematocyst firing. Scraping the affected skin, such as with the edge of a credit card, may remove remaining nematocysts. Once the skin has been cleaned of nematocysts, hydrocortisone cream applied locally reduces pain and inflammation. Antihistamines may help to control itching. Immunobased antivenins are used for serious box jellyfish stings.

 

In Elba Island and Corsica dittrichia viscosa is now used by residents and tourists to heal stings from jellyfish, bees and wasps pressing fresh leaves on the skin with quick results.

 

Mechanical issues

Jellyfish in large quantities can fill and split fishing nets and crush captured fish. They can clog cooling equipment, having disabled power stations in several countries; jellyfish caused a cascading blackout in the Philippines in 1999, as well as damaging the Diablo Canyon Power Plant in California in 2008. They can also stop desalination plants and ships' engines.

Jellyfish, also known sea jellies, are the medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria.

 

Jellyfish are mainly free-swimming marine animals with umbrella-shaped bells and trailing tentacles, although a few are anchored to the seabed by stalks rather than being mobile. The bell can pulsate to provide propulsion for highly efficient locomotion. The tentacles are armed with stinging cells and may be used to capture prey and defend against predators. Jellyfish have a complex life cycle. The medusa is normally the sexual phase, which produces planula larvae; these then disperse widely and enter a sedentary polyp phase, before reaching sexual maturity.

 

Jellyfish are found all over the world, from surface waters to the deep sea. Scyphozoans (the "true jellyfish") are exclusively marine, but some hydrozoans with a similar appearance live in freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide. The medusae of most species are fast-growing, and mature within a few months then die soon after breeding, but the polyp stage, attached to the seabed, may be much more long-lived. Jellyfish have been in existence for at least 500 million years, and possibly 700 million years or more, making them the oldest multi-organ animal group.

 

Jellyfish are eaten by humans in certain cultures. They are considered a delicacy in some Asian countries, where species in the Rhizostomeae order are pressed and salted to remove excess water. Australian researchers have described them as a "perfect food": sustainable and protein-rich but relatively low in food energy.

 

They are also used in research, where the green fluorescent protein used by some species to cause bioluminescence has been adapted as a fluorescent marker for genes inserted into other cells or organisms.

 

The stinging cells used by jellyfish to subdue their prey can injure humans. Thousands of swimmers worldwide are stung every year, with effects ranging from mild discomfort to serious injury or even death. When conditions are favourable, jellyfish can form vast swarms, which can be responsible for damage to fishing gear by filling fishing nets, and sometimes clog the cooling systems of power and desalination plants which draw their water from the sea.

  

Names

The name jellyfish, in use since 1796, has traditionally been applied to medusae and all similar animals including the comb jellies (ctenophores, another phylum). The term jellies or sea jellies is more recent, having been introduced by public aquaria in an effort to avoid use of the word "fish" with its modern connotation of an animal with a backbone, though shellfish, cuttlefish and starfish are not vertebrates either. In scientific literature, "jelly" and "jellyfish" have been used interchangeably. Many sources refer to only scyphozoans as "true jellyfish".

 

A group of jellyfish is called a "smack" or a "smuck".

 

Definition

The term jellyfish broadly corresponds to medusae, that is, a life-cycle stage in the Medusozoa. The American evolutionary biologist Paulyn Cartwright gives the following general definition:

 

Typically, medusozoan cnidarians have a pelagic, predatory jellyfish stage in their life cycle; staurozoans are the exceptions [as they are stalked].

 

The Merriam-Webster dictionary defines jellyfish as follows:

 

A free-swimming marine coelenterate that is the sexually reproducing form of a hydrozoan or scyphozoan and has a nearly transparent saucer-shaped body and extensible marginal tentacles studded with stinging cells.

 

Given that jellyfish is a common name, its mapping to biological groups is inexact. Some authorities have called the comb jellies and certain salps jellyfish, though other authorities state that neither of these are jellyfish, which they consider should be limited to certain groups within the medusozoa.

 

The non-medusozoan clades called jellyfish by some but not all authorities (both agreeing and disagreeing citations are given in each case) are indicated with on the following cladogram of the animal kingdom:

 

Jellyfish are not a clade, as they include most of the Medusozoa, barring some of the Hydrozoa. The medusozoan groups included by authorities are indicated on the following phylogenetic tree by the presence of citations. Names of included jellyfish, in English where possible, are shown in boldface; the presence of a named and cited example indicates that at least that species within its group has been called a jellyfish.

 

Taxonomy

The subphylum Medusozoa includes all cnidarians with a medusa stage in their life cycle. The basic cycle is egg, planula larva, polyp, medusa, with the medusa being the sexual stage. The polyp stage is sometimes secondarily lost. The subphylum include the major taxa, Scyphozoa (large jellyfish), Cubozoa (box jellyfish) and Hydrozoa (small jellyfish), and excludes Anthozoa (corals and sea anemones). This suggests that the medusa form evolved after the polyps. Medusozoans have tetramerous symmetry, with parts in fours or multiples of four.

 

The four major classes of medusozoan Cnidaria are:

Scyphozoa are sometimes called true jellyfish, though they are no more truly jellyfish than the others listed here. They have tetra-radial symmetry. Most have tentacles around the outer margin of the bowl-shaped bell, and long, oral arms around the mouth in the center of the subumbrella.

Cubozoa (box jellyfish) have a (rounded) box-shaped bell, and their velarium assists them to swim more quickly. Box jellyfish may be related more closely to scyphozoan jellyfish than either are to the Hydrozoa.

Hydrozoa medusae also have tetra-radial symmetry, nearly always have a velum (diaphragm used in swimming) attached just inside the bell margin, do not have oral arms, but a much smaller central stalk-like structure, the manubrium, with terminal mouth opening, and are distinguished by the absence of cells in the mesoglea. Hydrozoa show great diversity of lifestyle; some species maintain the polyp form for their entire life and do not form medusae at all (such as Hydra, which is hence not considered a jellyfish), and a few are entirely medusal and have no polyp form.

Staurozoa (stalked jellyfish) are characterized by a medusa form that is generally sessile, oriented upside down and with a stalk emerging from the apex of the "calyx" (bell), which attaches to the substrate. At least some Staurozoa also have a polyp form that alternates with the medusoid portion of the life cycle. Until recently, Staurozoa were classified within the Scyphozoa.

There are over 200 species of Scyphozoa, about 50 species of Staurozoa, about 50 species of Cubozoa, and the Hydrozoa includes about 1000–1500 species that produce medusae, but many more species that do not.

 

Fossil history

Since jellyfish have no hard parts, fossils are rare. The oldest unambiguous fossil of a free-swimming medusa is Burgessomedusa from the mid Cambrian Burgess Shale of Canada, which is likely either a stem group of box jellyfish (Cubozoa) or Acraspeda (the clade including Staurozoa, Cubozoa, and Scyphozoa). Other claimed records from the Cambrian of China and Utah in the United States are uncertain, and possibly represent ctenophores instead.

 

Anatomy

The main feature of a true jellyfish is the umbrella-shaped bell. This is a hollow structure consisting of a mass of transparent jelly-like matter known as mesoglea, which forms the hydrostatic skeleton of the animal. 95% or more of the mesogloea consists of water, but it also contains collagen and other fibrous proteins, as well as wandering amoebocytes which can engulf debris and bacteria. The mesogloea is bordered by the epidermis on the outside and the gastrodermis on the inside. The edge of the bell is often divided into rounded lobes known as lappets, which allow the bell to flex. In the gaps or niches between the lappets are dangling rudimentary sense organs known as rhopalia, and the margin of the bell often bears tentacles.

  

Anatomy of a scyphozoan jellyfish

On the underside of the bell is the manubrium, a stalk-like structure hanging down from the centre, with the mouth, which also functions as the anus, at its tip. There are often four oral arms connected to the manubrium, streaming away into the water below. The mouth opens into the gastrovascular cavity, where digestion takes place and nutrients are absorbed. This is subdivided by four thick septa into a central stomach and four gastric pockets. The four pairs of gonads are attached to the septa, and close to them four septal funnels open to the exterior, perhaps supplying good oxygenation to the gonads. Near the free edges of the septa, gastric filaments extend into the gastric cavity; these are armed with nematocysts and enzyme-producing cells and play a role in subduing and digesting the prey. In some scyphozoans, the gastric cavity is joined to radial canals which branch extensively and may join a marginal ring canal. Cilia in these canals circulate the fluid in a regular direction.

  

Discharge mechanism of a nematocyst

The box jellyfish is largely similar in structure. It has a squarish, box-like bell. A short pedalium or stalk hangs from each of the four lower corners. One or more long, slender tentacles are attached to each pedalium. The rim of the bell is folded inwards to form a shelf known as a velarium which restricts the bell's aperture and creates a powerful jet when the bell pulsates, allowing box jellyfish to swim faster than true jellyfish. Hydrozoans are also similar, usually with just four tentacles at the edge of the bell, although many hydrozoans are colonial and may not have a free-living medusal stage. In some species, a non-detachable bud known as a gonophore is formed that contains a gonad but is missing many other medusal features such as tentacles and rhopalia. Stalked jellyfish are attached to a solid surface by a basal disk, and resemble a polyp, the oral end of which has partially developed into a medusa with tentacle-bearing lobes and a central manubrium with four-sided mouth.

 

Most jellyfish do not have specialized systems for osmoregulation, respiration and circulation, and do not have a central nervous system. Nematocysts, which deliver the sting, are located mostly on the tentacles; true jellyfish also have them around the mouth and stomach. Jellyfish do not need a respiratory system because sufficient oxygen diffuses through the epidermis. They have limited control over their movement, but can navigate with the pulsations of the bell-like body; some species are active swimmers most of the time, while others largely drift. The rhopalia contain rudimentary sense organs which are able to detect light, water-borne vibrations, odour and orientation. A loose network of nerves called a "nerve net" is located in the epidermis. Although traditionally thought not to have a central nervous system, nerve net concentration and ganglion-like structures could be considered to constitute one in most species. A jellyfish detects stimuli, and transmits impulses both throughout the nerve net and around a circular nerve ring, to other nerve cells. The rhopalial ganglia contain pacemaker neurones which control swimming rate and direction.

 

In many species of jellyfish, the rhopalia include ocelli, light-sensitive organs able to tell light from dark. These are generally pigment spot ocelli, which have some of their cells pigmented. The rhopalia are suspended on stalks with heavy crystals at one end, acting like gyroscopes to orient the eyes skyward. Certain jellyfish look upward at the mangrove canopy while making a daily migration from mangrove swamps into the open lagoon, where they feed, and back again.

 

Box jellyfish have more advanced vision than the other groups. Each individual has 24 eyes, two of which are capable of seeing colour, and four parallel information processing areas that act in competition, supposedly making them one of the few kinds of animal to have a 360-degree view of its environment.

 

Box jellyfish eye

The study of jellyfish eye evolution is an intermediary to a better understanding of how visual systems evolved on Earth. Jellyfish exhibit immense variation in visual systems ranging from photoreceptive cell patches seen in simple photoreceptive systems to more derived complex eyes seen in box jellyfish. Major topics of jellyfish visual system research (with an emphasis on box jellyfish) include: the evolution of jellyfish vision from simple to complex visual systems), the eye morphology and molecular structures of box jellyfish (including comparisons to vertebrate eyes), and various uses of vision including task-guided behaviors and niche specialization.

 

Evolution

Experimental evidence for photosensitivity and photoreception in cnidarians antecedes the mid 1900s, and a rich body of research has since covered evolution of visual systems in jellyfish. Jellyfish visual systems range from simple photoreceptive cells to complex image-forming eyes. More ancestral visual systems incorporate extraocular vision (vision without eyes) that encompass numerous receptors dedicated to single-function behaviors. More derived visual systems comprise perception that is capable of multiple task-guided behaviors.

 

Although they lack a true brain, cnidarian jellyfish have a "ring" nervous system that plays a significant role in motor and sensory activity. This net of nerves is responsible for muscle contraction and movement and culminates the emergence of photosensitive structures. Across Cnidaria, there is large variation in the systems that underlie photosensitivity. Photosensitive structures range from non-specialized groups of cells, to more "conventional" eyes similar to those of vertebrates. The general evolutionary steps to develop complex vision include (from more ancestral to more derived states): non-directional photoreception, directional photoreception, low-resolution vision, and high-resolution vision. Increased habitat and task complexity has favored the high-resolution visual systems common in derived cnidarians such as box jellyfish.

 

Basal visual systems observed in various cnidarians exhibit photosensitivity representative of a single task or behavior. Extraocular photoreception (a form of non-directional photoreception), is the most basic form of light sensitivity and guides a variety of behaviors among cnidarians. It can function to regulate circadian rhythm (as seen in eyeless hydrozoans) and other light-guided behaviors responsive to the intensity and spectrum of light. Extraocular photoreception can function additionally in positive phototaxis (in planula larvae of hydrozoans), as well as in avoiding harmful amounts of UV radiation via negative phototaxis. Directional photoreception (the ability to perceive direction of incoming light) allows for more complex phototactic responses to light, and likely evolved by means of membrane stacking. The resulting behavioral responses can range from guided spawning events timed by moonlight to shadow responses for potential predator avoidance. Light-guided behaviors are observed in numerous scyphozoans including the common moon jelly, Aurelia aurita, which migrates in response to changes in ambient light and solar position even though they lack proper eyes.

 

The low-resolution visual system of box jellyfish is more derived than directional photoreception, and thus box jellyfish vision represents the most basic form of true vision in which multiple directional photoreceptors combine to create the first imaging and spatial resolution. This is different from the high-resolution vision that is observed in camera or compound eyes of vertebrates and cephalopods that rely on focusing optics. Critically, the visual systems of box jellyfish are responsible for guiding multiple tasks or behaviors in contrast to less derived visual systems in other jellyfish that guide single behavioral functions. These behaviors include phototaxis based on sunlight (positive) or shadows (negative), obstacle avoidance, and control of swim-pulse rate.

 

Box jellyfish possess "proper eyes" (similar to vertebrates) that allow them to inhabit environments that lesser derived medusae cannot. In fact, they are considered the only class in the clade Medusozoa that have behaviors necessitating spatial resolution and genuine vision. However, the lens in their eyes are more functionally similar to cup-eyes exhibited in low-resolution organisms, and have very little to no focusing capability. The lack of the ability to focus is due to the focal length exceeding the distance to the retina, thus generating unfocused images and limiting spatial resolution. The visual system is still sufficient for box jellyfish to produce an image to help with tasks such as object avoidance.

 

Utility as a model organism

Box jellyfish eyes are a visual system that is sophisticated in numerous ways. These intricacies include the considerable variation within the morphology of box jellyfishes' eyes (including their task/behavior specification), and the molecular makeup of their eyes including: photoreceptors, opsins, lenses, and synapses. The comparison of these attributes to more derived visual systems can allow for a further understanding of how the evolution of more derived visual systems may have occurred, and puts into perspective how box jellyfish can play the role as an evolutionary/developmental model for all visual systems.

 

Characteristics

Box jellyfish visual systems are both diverse and complex, comprising multiple photosystems. There is likely considerable variation in visual properties between species of box jellyfish given the significant inter-species morphological and physiological variation. Eyes tend to differ in size and shape, along with number of receptors (including opsins), and physiology across species of box jellyfish.

 

Box jellyfish have a series of intricate lensed eyes that are similar to those of more derived multicellular organisms such as vertebrates. Their 24 eyes fit into four different morphological categories. These categories consist of two large, morphologically different medial eyes (a lower and upper lensed eye) containing spherical lenses, a lateral pair of pigment slit eyes, and a lateral pair of pigment pit eyes. The eyes are situated on rhopalia (small sensory structures) which serve sensory functions of the box jellyfish and arise from the cavities of the exumbrella (the surface of the body) on the side of the bells of the jellyfish. The two large eyes are located on the mid-line of the club and are considered complex because they contain lenses. The four remaining eyes lie laterally on either side of each rhopalia and are considered simple. The simple eyes are observed as small invaginated cups of epithelium that have developed pigmentation. The larger of the complex eyes contains a cellular cornea created by a mono ciliated epithelium, cellular lens, homogenous capsule to the lens, vitreous body with prismatic elements, and a retina of pigmented cells. The smaller of the complex eyes is said to be slightly less complex given that it lacks a capsule but otherwise contains the same structure as the larger eye.

 

Box jellyfish have multiple photosystems that comprise different sets of eyes. Evidence includes immunocytochemical and molecular data that show photopigment differences among the different morphological eye types, and physiological experiments done on box jellyfish to suggest behavioral differences among photosystems. Each individual eye type constitutes photosystems that work collectively to control visually guided behaviors.

 

Box jellyfish eyes primarily use c-PRCs (ciliary photoreceptor cells) similar to that of vertebrate eyes. These cells undergo phototransduction cascades (process of light absorption by photoreceptors) that are triggered by c-opsins. Available opsin sequences suggest that there are two types of opsins possessed by all cnidarians including an ancient phylogenetic opsin, and a sister ciliary opsin to the c-opsins group. Box jellyfish could have both ciliary and cnidops (cnidarian opsins), which is something not previously believed to appear in the same retina. Nevertheless, it is not entirely evident whether cnidarians possess multiple opsins that are capable of having distinctive spectral sensitivities.

 

Comparison with other organisms

Comparative research on genetic and molecular makeup of box jellyfishes' eyes versus more derived eyes seen in vertebrates and cephalopods focuses on: lenses and crystallin composition, synapses, and Pax genes and their implied evidence for shared primordial (ancestral) genes in eye evolution.

 

Box jellyfish eyes are said to be an evolutionary/developmental model of all eyes based on their evolutionary recruitment of crystallins and Pax genes. Research done on box jellyfish including Tripedalia cystophora has suggested that they possess a single Pax gene, PaxB. PaxB functions by binding to crystallin promoters and activating them. PaxB in situ hybridization resulted in PaxB expression in the lens, retina, and statocysts. These results and the rejection of the prior hypothesis that Pax6 was an ancestral Pax gene in eyes has led to the conclusion that PaxB was a primordial gene in eye evolution, and that the eyes of all organisms likely share a common ancestor.

 

The lens structure of box jellyfish appears very similar to those of other organisms, but the crystallins are distinct in both function and appearance. Weak reactions were seen within the sera and there were very weak sequence similarities within the crystallins among vertebrate and invertebrate lenses. This is likely due to differences in lower molecular weight proteins and the subsequent lack of immunological reactions with antisera that other organisms' lenses exhibit.

 

All four of the visual systems of box jellyfish species investigated with detail (Carybdea marsupialis, Chiropsalmus quadrumanus, Tamoya haplonema and Tripedalia cystophora) have invaginated synapses, but only in the upper and lower lensed eyes. Different densities were found between the upper and lower lenses, and between species. Four types of chemical synapses have been discovered within the rhopalia which could help in understanding neural organization including: clear unidirectional, dense-core unidirectional, clear bidirectional, and clear and dense-core bidirectional. The synapses of the lensed eyes could be useful as markers to learn more about the neural circuit in box jellyfish retinal areas.

 

Evolution as a response to natural stimuli

The primary adaptive responses to environmental variation observed in box jellyfish eyes include pupillary constriction speeds in response to light environments, as well as photoreceptor tuning and lens adaptations to better respond to shifts between light environments and darkness. Interestingly, some box jellyfish species' eyes appear to have evolved more focused vision in response to their habitat.

 

Pupillary contraction appears to have evolved in response to variation in the light environment across ecological niches across three species of box jellyfish (Chironex fleckeri, Chiropsella bronzie, and Carukia barnesi). Behavioral studies suggest that faster pupil contraction rates allow for greater object avoidance, and in fact, species with more complex habitats exhibit faster rates. Ch. bronzie inhabit shallow beach fronts that have low visibility and very few obstacles, thus, faster pupil contraction in response to objects in their environment is not important. Ca. barnesi and Ch. fleckeri are found in more three-dimensionally complex environments like mangroves with an abundance of natural obstacles, where faster pupil contraction is more adaptive. Behavioral studies support the idea that faster pupillary contraction rates assist with obstacle avoidance as well as depth adjustments in response to differing light intensities.

 

Light/dark adaptation via pupillary light reflexes is an additional form of an evolutionary response to the light environment. This relates to the pupil's response to shifts between light intensity (generally from sunlight to darkness). In the process of light/dark adaptation, the upper and lower lens eyes of different box jellyfish species vary in specific function. The lower lens-eyes contain pigmented photoreceptors and long pigment cells with dark pigments that migrate on light/dark adaptation, while the upper-lens eyes play a concentrated role in light direction and phototaxis given that they face upward towards the water surface (towards the sun or moon). The upper lens of Ch. bronzie does not exhibit any considerable optical power while Tr. cystophora (a box jellyfish species that tends to live in mangroves) does. The ability to use light to visually guide behavior is not of as much importance to Ch. bronzie as it is to species in more obstacle-filled environments. Differences in visually guided behavior serve as evidence that species that share the same number and structure of eyes can exhibit differences in how they control behavior.

 

Largest and smallest

Jellyfish range from about one millimeter in bell height and diameter, to nearly 2 metres (6+1⁄2 ft) in bell height and diameter; the tentacles and mouth parts usually extend beyond this bell dimension.

 

The smallest jellyfish are the peculiar creeping jellyfish in the genera Staurocladia and Eleutheria, which have bell disks from 0.5 millimetres (1⁄32 in) to a few millimeters in diameter, with short tentacles that extend out beyond this, which these jellyfish use to move across the surface of seaweed or the bottoms of rocky pools; many of these tiny creeping jellyfish cannot be seen in the field without a hand lens or microscope. They can reproduce asexually by fission (splitting in half). Other very small jellyfish, which have bells about one millimeter, are the hydromedusae of many species that have just been released from their parent polyps; some of these live only a few minutes before shedding their gametes in the plankton and then dying, while others will grow in the plankton for weeks or months. The hydromedusae Cladonema radiatum and Cladonema californicum are also very small, living for months, yet never growing beyond a few mm in bell height and diameter.

 

The lion's mane jellyfish, Cyanea capillata, was long-cited as the largest jellyfish, and arguably the longest animal in the world, with fine, thread-like tentacles that may extend up to 36.5 m (119 ft 9 in) long (though most are nowhere near that large). They have a moderately painful, but rarely fatal, sting. The increasingly common giant Nomura's jellyfish, Nemopilema nomurai, found in some, but not all years in the waters of Japan, Korea and China in summer and autumn is another candidate for "largest jellyfish", in terms of diameter and weight, since the largest Nomura's jellyfish in late autumn can reach 2 m (6 ft 7 in) in bell (body) diameter and about 200 kg (440 lb) in weight, with average specimens frequently reaching 0.9 m (2 ft 11 in) in bell diameter and about 150 kg (330 lb) in weight. The large bell mass of the giant Nomura's jellyfish can dwarf a diver and is nearly always much greater than the Lion's Mane, whose bell diameter can reach 1 m (3 ft 3 in).

 

The rarely encountered deep-sea jellyfish Stygiomedusa gigantea is another candidate for "largest jellyfish", with its thick, massive bell up to 100 cm (3 ft 3 in) wide, and four thick, "strap-like" oral arms extending up to 6 m (19+1⁄2 ft) in length, very different from the typical fine, threadlike tentacles that rim the umbrella of more-typical-looking jellyfish, including the Lion's Mane.

 

Desmonema glaciale, which lives in the Antarctic region, can reach a very large size (several meters). Purple-striped jelly (Chrysaora colorata) can also be extremely long (up to 15 feet).

 

Life history and behavior

Life cycle

Jellyfish have a complex life cycle which includes both sexual and asexual phases, with the medusa being the sexual stage in most instances. Sperm fertilize eggs, which develop into larval planulae, become polyps, bud into ephyrae and then transform into adult medusae. In some species certain stages may be skipped.

 

Upon reaching adult size, jellyfish spawn regularly if there is a sufficient supply of food. In most species, spawning is controlled by light, with all individuals spawning at about the same time of day; in many instances this is at dawn or dusk. Jellyfish are usually either male or female (with occasional hermaphrodites). In most cases, adults release sperm and eggs into the surrounding water, where the unprotected eggs are fertilized and develop into larvae. In a few species, the sperm swim into the female's mouth, fertilizing the eggs within her body, where they remain during early development stages. In moon jellies, the eggs lodge in pits on the oral arms, which form a temporary brood chamber for the developing planula larvae.

 

The planula is a small larva covered with cilia. When sufficiently developed, it settles onto a firm surface and develops into a polyp. The polyp generally consists of a small stalk topped by a mouth that is ringed by upward-facing tentacles. The polyps resemble those of closely related anthozoans, such as sea anemones and corals. The jellyfish polyp may be sessile, living on the bottom, boat hulls or other substrates, or it may be free-floating or attached to tiny bits of free-living plankton or rarely, fish or other invertebrates. Polyps may be solitary or colonial. Most polyps are only millimetres in diameter and feed continuously. The polyp stage may last for years.

 

After an interval and stimulated by seasonal or hormonal changes, the polyp may begin reproducing asexually by budding and, in the Scyphozoa, is called a segmenting polyp, or a scyphistoma. Budding produces more scyphistomae and also ephyrae. Budding sites vary by species; from the tentacle bulbs, the manubrium (above the mouth), or the gonads of hydromedusae. In a process known as strobilation, the polyp's tentacles are reabsorbed and the body starts to narrow, forming transverse constrictions, in several places near the upper extremity of the polyp. These deepen as the constriction sites migrate down the body, and separate segments known as ephyra detach. These are free-swimming precursors of the adult medusa stage, which is the life stage that is typically identified as a jellyfish. The ephyrae, usually only a millimeter or two across initially, swim away from the polyp and grow. Limnomedusae polyps can asexually produce a creeping frustule larval form, which crawls away before developing into another polyp. A few species can produce new medusae by budding directly from the medusan stage. Some hydromedusae reproduce by fission.

 

Lifespan

Little is known of the life histories of many jellyfish as the places on the seabed where the benthic forms of those species live have not been found. However, an asexually reproducing strobila form can sometimes live for several years, producing new medusae (ephyra larvae) each year.

 

An unusual species, Turritopsis dohrnii, formerly classified as Turritopsis nutricula, might be effectively immortal because of its ability under certain circumstances to transform from medusa back to the polyp stage, thereby escaping the death that typically awaits medusae post-reproduction if they have not otherwise been eaten by some other organism. So far this reversal has been observed only in the laboratory.

 

Locomotion

Jellyfish locomotion is highly efficient. Muscles in the jellylike bell contract, setting up a start vortex and propelling the animal. When the contraction ends, the bell recoils elastically, creating a stop vortex with no extra energy input.

Using the moon jelly Aurelia aurita as an example, jellyfish have been shown to be the most energy-efficient swimmers of all animals. They move through the water by radially expanding and contracting their bell-shaped bodies to push water behind them. They pause between the contraction and expansion phases to create two vortex rings. Muscles are used for the contraction of the body, which creates the first vortex and pushes the animal forward, but the mesoglea is so elastic that the expansion is powered exclusively by relaxing the bell, which releases the energy stored from the contraction. Meanwhile, the second vortex ring starts to spin faster, sucking water into the bell and pushing against the centre of the body, giving a secondary and "free" boost forward. The mechanism, called passive energy recapture, only works in relatively small jellyfish moving at low speeds, allowing the animal to travel 30 percent farther on each swimming cycle. Jellyfish achieved a 48 percent lower cost of transport (food and oxygen intake versus energy spent in movement) than other animals in similar studies. One reason for this is that most of the gelatinous tissue of the bell is inactive, using no energy during swimming.

 

Ecology

Diet

Jellyfish are, like other cnidarians, generally carnivorous (or parasitic), feeding on planktonic organisms, crustaceans, small fish, fish eggs and larvae, and other jellyfish, ingesting food and voiding undigested waste through the mouth. They hunt passively using their tentacles as drift lines, or sink through the water with their tentacles spread widely; the tentacles, which contain nematocysts to stun or kill the prey, may then flex to help bring it to the mouth. Their swimming technique also helps them to capture prey; when their bell expands it sucks in water which brings more potential prey within reach of the tentacles.

 

A few species such as Aglaura hemistoma are omnivorous, feeding on microplankton which is a mixture of zooplankton and phytoplankton (microscopic plants) such as dinoflagellates. Others harbour mutualistic algae (Zooxanthellae) in their tissues; the spotted jellyfish (Mastigias papua) is typical of these, deriving part of its nutrition from the products of photosynthesis, and part from captured zooplankton. The upside-down jellyfish (Cassiopea andromeda) also has a symbiotic relationship with microalgae, but captures tiny animals to supplement their diet. This is done by releasing tiny balls of living cells composed of mesoglea. These use cilia to drive them through water and stinging cells which stun the prey. The blobs also seems to have digestive capabilities.

 

Predation

Other species of jellyfish are among the most common and important jellyfish predators. Sea anemones may eat jellyfish that drift into their range. Other predators include tunas, sharks, swordfish, sea turtles and penguins. Jellyfish washed up on the beach are consumed by foxes, other terrestrial mammals and birds. In general however, few animals prey on jellyfish; they can broadly be considered to be top predators in the food chain. Once jellyfish have become dominant in an ecosystem, for example through overfishing which removes predators of jellyfish larvae, there may be no obvious way for the previous balance to be restored: they eat fish eggs and juvenile fish, and compete with fish for food, preventing fish stocks from recovering.

 

Symbiosis

Some small fish are immune to the stings of the jellyfish and live among the tentacles, serving as bait in a fish trap; they are safe from potential predators and are able to share the fish caught by the jellyfish. The cannonball jellyfish has a symbiotic relationship with ten different species of fish, and with the longnose spider crab, which lives inside the bell, sharing the jellyfish's food and nibbling its tissues.

 

Main article: Jellyfish bloom

Jellyfish form large masses or blooms in certain environmental conditions of ocean currents, nutrients, sunshine, temperature, season, prey availability, reduced predation and oxygen concentration. Currents collect jellyfish together, especially in years with unusually high populations. Jellyfish can detect marine currents and swim against the current to congregate in blooms. Jellyfish are better able to survive in nutrient-rich, oxygen-poor water than competitors, and thus can feast on plankton without competition. Jellyfish may also benefit from saltier waters, as saltier waters contain more iodine, which is necessary for polyps to turn into jellyfish. Rising sea temperatures caused by climate change may also contribute to jellyfish blooms, because many species of jellyfish are able to survive in warmer waters. Increased nutrients from agricultural or urban runoff with nutrients including nitrogen and phosphorus compounds increase the growth of phytoplankton, causing eutrophication and algal blooms. When the phytoplankton die, they may create dead zones, so-called because they are hypoxic (low in oxygen). This in turn kills fish and other animals, but not jellyfish, allowing them to bloom. Jellyfish populations may be expanding globally as a result of land runoff and overfishing of their natural predators. Jellyfish are well placed to benefit from disturbance of marine ecosystems. They reproduce rapidly; they prey upon many species, while few species prey on them; and they feed via touch rather than visually, so they can feed effectively at night and in turbid waters. It may be difficult for fish stocks to re-establish themselves in marine ecosystems once they have become dominated by jellyfish, because jellyfish feed on plankton, which includes fish eggs and larvae.

 

As suspected at the turn of this century, jellyfish blooms are increasing in frequency. Between 2013 and 2020 the Mediterranean Science Commission monitored on a weekly basis the frequency of such outbreaks in coastal waters from Morocco to the Black Sea, revealing a relatively high frequency of these blooms nearly all year round, with peaks observed from March to July and often again in the autumn. The blooms are caused by different jellyfish species, depending on their localisation within the Basin: one observes a clear dominance of Pelagia noctiluca and Velella velella outbreaks in the western Mediterranean, of Rhizostoma pulmo and Rhopilema nomadica outbreaks in the eastern Mediterranean, and of Aurelia aurita and Mnemiopsis leidyi outbreaks in the Black Sea.

 

Some jellyfish populations that have shown clear increases in the past few decades are invasive species, newly arrived from other habitats: examples include the Black Sea, Caspian Sea, Baltic Sea, central and eastern Mediterranean, Hawaii, and tropical and subtropical parts of the West Atlantic (including the Caribbean, Gulf of Mexico and Brazil).

 

Jellyfish blooms can have significant impact on community structure. Some carnivorous jellyfish species prey on zooplankton while others graze on primary producers. Reductions in zooplankton and ichthyoplankton due to a jellyfish bloom can ripple through the trophic levels. High-density jellyfish populations can outcompete other predators and reduce fish recruitment. Increased grazing on primary producers by jellyfish can also interrupt energy transfer to higher trophic levels.

 

During blooms, jellyfish significantly alter the nutrient availability in their environment. Blooms require large amounts of available organic nutrients in the water column to grow, limiting availability for other organisms. Some jellyfish have a symbiotic relationship with single-celled dinoflagellates, allowing them to assimilate inorganic carbon, phosphorus, and nitrogen creating competition for phytoplankton. Their large biomass makes them an important source of dissolved and particulate organic matter for microbial communities through excretion, mucus production, and decomposition. The microbes break down the organic matter into inorganic ammonium and phosphate. However, the low carbon availability shifts the process from production to respiration creating low oxygen areas making the dissolved inorganic nitrogen and phosphorus largely unavailable for primary production.

 

These blooms have very real impacts on industries. Jellyfish can outcompete fish by utilizing open niches in over-fished fisheries. Catch of jellyfish can strain fishing gear and lead to expenses relating to damaged gear. Power plants have been shut down due to jellyfish blocking the flow of cooling water. Blooms have also been harmful for tourism, causing a rise in stings and sometimes the closure of beaches.

 

Jellyfish form a component of jelly-falls, events where gelatinous zooplankton fall to the seafloor, providing food for the benthic organisms there. In temperate and subpolar regions, jelly-falls usually follow immediately after a bloom.

 

Habitats

Most jellyfish are marine animals, although a few hydromedusae inhabit freshwater. The best known freshwater example is the cosmopolitan hydrozoan jellyfish, Craspedacusta sowerbii. It is less than an inch (2.5 cm) in diameter, colorless and does not sting. Some jellyfish populations have become restricted to coastal saltwater lakes, such as Jellyfish Lake in Palau. Jellyfish Lake is a marine lake where millions of golden jellyfish (Mastigias spp.) migrate horizontally across the lake daily.

 

Although most jellyfish live well off the ocean floor and form part of the plankton, a few species are closely associated with the bottom for much of their lives and can be considered benthic. The upside-down jellyfish in the genus Cassiopea typically lie on the bottom of shallow lagoons where they sometimes pulsate gently with their umbrella top facing down. Even some deep-sea species of hydromedusae and scyphomedusae are usually collected on or near the bottom. All of the stauromedusae are found attached to either seaweed or rocky or other firm material on the bottom.

 

Some species explicitly adapt to tidal flux. In Roscoe Bay, jellyfish ride the current at ebb tide until they hit a gravel bar, and then descend below the current. They remain in still waters until the tide rises, ascending and allowing it to sweep them back into the bay. They also actively avoid fresh water from mountain snowmelt, diving until they find enough salt.

  

Parasites

Jellyfish are hosts to a wide variety of parasitic organisms. They act as intermediate hosts of endoparasitic helminths, with the infection being transferred to the definitive host fish after predation. Some digenean trematodes, especially species in the family Lepocreadiidae, use jellyfish as their second intermediate hosts. Fish become infected by the trematodes when they feed on infected jellyfish.

 

Relation to humans

Jellyfish have long been eaten in some parts of the world. Fisheries have begun harvesting the American cannonball jellyfish, Stomolophus meleagris, along the southern Atlantic coast of the United States and in the Gulf of Mexico for export to Asia.

 

Jellyfish are also harvested for their collagen, which is being investigated for use in a variety of applications including the treatment of rheumatoid arthritis.

 

Aquaculture and fisheries of other species often suffer severe losses – and so losses of productivity – due to jellyfish.

 

Products

Main article: Jellyfish as food

In some countries, including China, Japan, and Korea, jellyfish are a delicacy. The jellyfish is dried to prevent spoiling. Only some 12 species of scyphozoan jellyfish belonging to the order Rhizostomeae are harvested for food, mostly in southeast Asia. Rhizostomes, especially Rhopilema esculentum in China (海蜇 hǎizhé, 'sea stingers') and Stomolophus meleagris (cannonball jellyfish) in the United States, are favored because of their larger and more rigid bodies and because their toxins are harmless to humans.

 

Traditional processing methods, carried out by a jellyfish master, involve a 20- to 40-day multi-phase procedure in which, after removing the gonads and mucous membranes, the umbrella and oral arms are treated with a mixture of table salt and alum, and compressed. Processing makes the jellyfish drier and more acidic, producing a crisp texture. Jellyfish prepared this way retain 7–10% of their original weight, and the processed product consists of approximately 94% water and 6% protein. Freshly processed jellyfish has a white, creamy color and turns yellow or brown during prolonged storage.

 

In China, processed jellyfish are desalted by soaking in water overnight and eaten cooked or raw. The dish is often served shredded with a dressing of oil, soy sauce, vinegar and sugar, or as a salad with vegetables. In Japan, cured jellyfish are rinsed, cut into strips and served with vinegar as an appetizer. Desalted, ready-to-eat products are also available.

 

Biotechnology

The hydromedusa Aequorea victoria was the source of green fluorescent protein, studied for its role in bioluminescence and later for use as a marker in genetic engineering.

Pliny the Elder reported in his Natural History that the slime of the jellyfish "Pulmo marinus" produced light when rubbed on a walking stick.

 

In 1961, Osamu Shimomura extracted green fluorescent protein (GFP) and another bioluminescent protein, called aequorin, from the large and abundant hydromedusa Aequorea victoria, while studying photoproteins that cause bioluminescence in this species. Three decades later, Douglas Prasher sequenced and cloned the gene for GFP. Martin Chalfie figured out how to use GFP as a fluorescent marker of genes inserted into other cells or organisms. Roger Tsien later chemically manipulated GFP to produce other fluorescent colors to use as markers. In 2008, Shimomura, Chalfie and Tsien won the Nobel Prize in Chemistry for their work with GFP. Man-made GFP became widely used as a fluorescent tag to show which cells or tissues express specific genes. The genetic engineering technique fuses the gene of interest to the GFP gene. The fused DNA is then put into a cell, to generate either a cell line or (via IVF techniques) an entire animal bearing the gene. In the cell or animal, the artificial gene turns on in the same tissues and the same time as the normal gene, making a fusion of the normal protein with GFP attached to the end, illuminating the animal or cell reveals what tissues express that protein—or at what stage of development. The fluorescence shows where the gene is expressed.

 

Aquarium display

Jellyfish are displayed in many public aquariums. Often the tank's background is blue and the animals are illuminated by side light, increasing the contrast between the animal and the background. In natural conditions, many jellies are so transparent that they are nearly invisible. Jellyfish are not adapted to closed spaces. They depend on currents to transport them from place to place. Professional exhibits as in the Monterey Bay Aquarium feature precise water flows, typically in circular tanks to avoid trapping specimens in corners. The outflow is spread out over a large surface area and the inflow enters as a sheet of water in front of the outflow, so the jellyfish do not get sucked into it. As of 2009, jellyfish were becoming popular in home aquariums, where they require similar equipment.

 

Stings

Jellyfish are armed with nematocysts, a type of specialized stinging cell. Contact with a jellyfish tentacle can trigger millions of nematocysts to pierce the skin and inject venom, but only some species' venom causes an adverse reaction in humans. In a study published in Communications Biology, researchers found a jellyfish species called Cassiopea xamachana which when triggered will release tiny balls of cells that swim around the jellyfish stinging everything in their path. Researchers described these as "self-propelling microscopic grenades" and named them cassiosomes.

 

The effects of stings range from mild discomfort to extreme pain and death. Most jellyfish stings are not deadly, but stings of some box jellyfish (Irukandji jellyfish), such as the sea wasp, can be deadly. Stings may cause anaphylaxis (a form of shock), which can be fatal. Jellyfish kill 20 to 40 people a year in the Philippines alone. In 2006 the Spanish Red Cross treated 19,000 stung swimmers along the Costa Brava.

 

Vinegar (3–10% aqueous acetic acid) may help with box jellyfish stings but not the stings of the Portuguese man o' war. Clearing the area of jelly and tentacles reduces nematocyst firing. Scraping the affected skin, such as with the edge of a credit card, may remove remaining nematocysts. Once the skin has been cleaned of nematocysts, hydrocortisone cream applied locally reduces pain and inflammation. Antihistamines may help to control itching. Immunobased antivenins are used for serious box jellyfish stings.

 

In Elba Island and Corsica dittrichia viscosa is now used by residents and tourists to heal stings from jellyfish, bees and wasps pressing fresh leaves on the skin with quick results.

 

Mechanical issues

Jellyfish in large quantities can fill and split fishing nets and crush captured fish. They can clog cooling equipment, having disabled power stations in several countries; jellyfish caused a cascading blackout in the Philippines in 1999, as well as damaging the Diablo Canyon Power Plant in California in 2008. They can also stop desalination plants and ships' engines.

This Lego Technic MOC was built special for LEGO Technic Mercedes-Benz Future Truck competition. The goal: to construct Mercedes-Benz truck of the 2045 year. So it’s my version - Multifunctional Truck Platform. This model is based on six-wheel AWD module with full independent suspension and outriggers (2xXL motors, dimensions – 48x23x9 cm, total weight – 1580 g). The module is pilotless and it has electric motors. The cabin is just an option because the modules can be united and there is no need to have the cabin in each module. The module has zero turning radius. It can be remote controlled at distance up to 1,5 km for local maneuvering. The wide range of the rigs can be mounted on it. I’ve built the truck body and the excavator for instance. The truck body has all-side unloading; it’s very comfortable at narrow building areas. The excavator has one extra function – an extensible boom. So it has very high performance and wide range of working.

Video: youtu.be/oT8P-Nl7nh4

PHILIPPINE SEA (Sept. 27, 2021) Sailors guide an 11-meter rigid hull inflatable boat during a twin boom extensible crane training evolution in the mission bay aboard Independence-variant littoral combat ship USS Charleston (LCS 18). Charleston, part of Destroyer Squadron 7, is on a rotational deployment, operating in the U.S. 7th Fleet to enhance interoperability with partners and serve as a ready-response force in support of a free and open Indo-Pacific region. (U.S. Navy photo by Mass Communication Specialist 2nd Class Ryan M. Breeden)

Varsovia escribiu páxinas decisivas na historia do pasado século. Gueto xudeu, invasión alemá e rusa, holocausto, usurpación de Estado durante 123 anos , guerras e máis guerras e dominios externos extensibles ao resto do país de Polonia. As testemuñas que avalan estes feitos sucédense ao longo da cidade.

Hoxe a Varsovia restaurada con mimo ,é unha cidade moderna que se despereza dun longo letargo e reincorpórase a Europa , ou polo menos iso parece, aínda que mantén un distancia prudencial , que non se se é propia do espírito de desconfianza que se vive na súa sociedade ou pola propia crise de identidade dunha Europa que non se atopa a se mesma

Imbrium Lunokhod Industries Model VS-MU-333 'Lorikeet' is the next step in Imbrium Lunokhod Industries Frame System. This mass produced frame builds on the versatile and flexible mobile frame platform made popular by the VS-M/S-71 'Degei' (flic.kr/s/aHsm37uTTm) and the VS-MX-04 'Rangi' (flic.kr/s/aHsk4AUkEY). Developed for planetary surface operations and utility deployments, the Lorikeet will definitely not excel in zero-g environments, it's outclassed by more maneuverable specialty frames. But for deployments to planetary surfaces, the frame offers a more affordable (although less durable) alternative to the Varuna (flic.kr/s/aHsm89p5MW) the a more extensible (and repairable) alternative to the Krivlyaka (flic.kr/s/aHsm4d6e2v).

 

From a design perspective, the frame takes a ton of inspiration from both Malcolm Craig's MgN-333 (flic.kr/p/dEFocc) and Aardvark17's Budgie (flic.kr/p/2kgyyua) frames as well as my version of the HR-13 flic.kr/s/aHsmMLcB3m.

 

===========================================================

Built for Mobile Frame Zero - a tabletop wargame.

Mobile Frame Hangar Nova (MFZ Community Forums).

===========================================================

Detall preciós del visor de la Plaubel Makina II. Consta d'una part frontal amb una lent que proporciona el mateix angular que la lent principal d'aquestes càmeres, 100mm. La part posterior es pot moure en diagonal, compensant la paral·laxi fins a 1.5 m. Igualment té un tint blau, crec que per acostar la gama cromatica a la sensibilitat dels negatius ortocromatics de pre guerra, insensibles al vermell.

 

La Plaubel Makina II és una càmara de gran format de meitat del s. XX, extensible i destinada sobretot a la premsa. Feia servir plaques de 6,5x9cm però s'adapta sense problemes a porta-rodets de format 120, com en el cas d'aquesta.

 

Les primeres Makina no tenien telèmetre, però a partir de la Makina II del 1933 ja incorpora un. Posteriorment es refinarà el model amb la Makina IIS, que facilita molt el canvi de lents, i ja després de la guerra mundial, l'ultim model és la Makina III, amb molts canvis sobretot per a disparar flaix.

 

De fet, aquesta que tinc és una mica inusual ja que no sembla pas una Makina IIS per tal i com està montada la lent. De fet té dues parts, amb el obturador al mig, el que fa més dificil desmontar-la. Però en canvi té les dues finestretes del telèmetre rectangulars, el que és un element distintiu de les IIS. Probablement sigui una II a la que es va reformar el telèmetre per alguna raó, o bé es tracti d'un model just de transició. El que si no milloraren fou una refotuda manera d'agafar-la. Ergonomía? no en tenien ni idea!!

 

En tot cas és clàrament anterior a la guerra (ja que està marcada amb el DRP "Deutsches Reich Patent" en comptes del DBP de postguerra, "Deutsches BundesPatent". Crec que fou fabricada entre el 1933 i el 1936, més aviat cap al final del periode, ja que el frontal és cromat, i inicialment es produia en negre. Potser fou una de les darreres Makina II (abans del canvi al model IIS) i per això 1936 sembla la data més probable de producció.

 

==================

 

Precious detail of the viewfinder of the Plaubel Makina II. It consists of a front part that provides the same angle as the main lens of these cameras, 100mm. The rear part can be moved diagonally, compensating parallax up to 1.5 m. It also has a blue dye, I think that it brings the chromatic range to the sensitivity of the orthochromatic negatives of pre-war, insensitive to the red.

 

The Plaubel Makina II is a large format press camera from the 30's to 50's, strut-folding. It used 6.5x9cm glass plates but also 120 format backs, as this one.

 

The first Makina had no rangefinder, but in 1933 the Makina II already incorporates one. Later, the model will be refined with the Makina II S, which greatly facilitates the change of lens, and even after the World War, the latest model is the Makina III, with many refinements, especially for flash synchro. What they didn't get at all was an easy way to hold it. Ergonomics, what's that??

 

In fact, this one that I have is a little unusual since it does not look like a Makina IIS as the lens has two parts, with the shutter in the middle, which makes it more difficult to disassemble it. But otherwise it has rangefinder rectangular windows, which is a distinctive element of the IIS. It is probably a II to which the rangefinder was reformed for some reason, or it was just a transition model.

 

In any case, it was clearly made before WW2 (since it is marked with the DRP "Deutsches Reich Patent" instead of the post-war DBP, "Deutsches BundesPatent.") I think it was manufactured between 1933 and 1936, rather towards the end of this period, since the front is chromed, and initially it was produced in black. Perhaps it was one of the last Makina II (before the change to the IIS model) and for that reason 1936 seems the most probable date of production.

 

lommen9.home.xs4all.nl/plaubel/index.html

 

www.earlyphotography.co.uk/site/entry_C25.html

 

camera-wiki.org/wiki/Plaubel_Makina#The_6.5.C3.979_rangef...

 

A wild tangent inspired by Dominik Strzelec's Processing demo of catenary curves in Toxiclibs.

 

I was curious about the simulation aspect and how it might relate to parametric modeling, but then I added some basic color shading and promptly forgot about everything else. Sketches like these don't really have a defined place in my current practice and I usually only get to show them in lectures, so by now I have a growing elephant graveyard of code sketches like these.

 

I'm embarrassed to say this is the first time I've seriously used Toxiclibs for more than 20 minutes. It really is a thing of beauty and contains some very powerful tools once you figure out Karsten's code structure. Most coders tend towards idiosyncracy and Karsten is no exception, but his manifests itself in the form of well-thought out and extensible code structures while mine are far less elegant.

 

I plan to post a version of my sketch on OpenProcessing as a nod to Dominik for using his code. The physical simulation is still Toxiclibs, but I've moved all rendering, GUI and meshing to Modelbuilder for my own convenience's sake.

Metabolism's most monumental treatment was naturally at the hands of Tange, who, before he godfathered the movement, had already demonstrated his interest in reconciling up-to-the-minute Modernism with traditional carpentry and monumental form. Moreso than his roughly contemporaneous Shizuoka Press building, the Yamanashi building, seen here, teeters between the promise of Metabolist-megastructural extensibility and the rigidity of a Brutalist solid. With this in mind, note the pronounced symmetry, and the decision to use the same concrete material palette for both the "cores" and the connecting bridges of program - which makes a hash out of the Metabolist conceit of semi-permanent cores (tree-trunks) supporting transient program (leaves). These indicators of a monumental formalism outweigh the admittedly important fact that Tange had wanted this to be a bit "emptier," to better suggest the incompleteness of its matrix and imply later expansion. The client, I suppose, didn't go for the idea of building more framework than their building actually required - but even allowing for this, the buiding seems rather less poised to expand and change than others of its ilk. Certainly there is no pretense here of potentially demounting the built pieces.

 

These aren't faults, and by the way, if you haven't noticed, this thing is fabulous. I just want to emphasize that Tange's interests lay with architecture's role as symbolic form, and its capacity to create landmarks relevant to their point in modern history. Fuji TV lies on this same trajectory, a few years later; compare also to Raj Rewal's work in this vein. But as far as "growth and change" go, the relatively disposable cars, buses, and vending machines at this building's feet are closer to Metabolism than any building could hope to be.

 

(For more on Metabolism's conceptual hurdles, see my Nakagin Capsule Tower text.)

Bats are mammals of the order Chiroptera (/kaɪˈrɒptərə/; from the Greek χείρ - cheir, "hand" and πτερόν - pteron, "wing") whose forelimbs form webbed wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums, and colugos, can only glide for short distances. Bats do not flap their entire forelimbs, as birds do, but instead flap their spread-out digits, which are very long and covered with a thin membrane or patagium.

 

Bats are the second largest order of mammals (after the rodents), representing about 20% of all classified mammal species worldwide, with about 1,240 bat species divided into two suborders: the less specialized and largely fruit-eating megabats, or flying foxes, and the highly specialized and echolocating microbats. About 70% of bat species are insectivores. Most of the rest are frugivores, or fruit eaters. A few species, such as the fish-eating bat, feed from animals other than insects, with the vampire bats being hematophagous, or feeding on blood.

 

Bats are present throughout most of the world, with the exception of extremely cold regions. They perform vital ecological roles of pollinating flowers and dispersing fruit seeds; many tropical plant species depend entirely on bats for the distribution of their seeds. Bats are economically important, as they consume insect pests, reducing the need for pesticides. The smallest bat is the Kitti's hog-nosed bat, measuring 29–34 mm in length, 15 cm across the wings and 2–2.6 g in mass. It is also arguably the smallest extant species of mammal, with the Etruscan shrew being the other contender. The largest species of bat are a few species of Pteropus (fruit bats or flying foxes) and the giant golden-crowned flying fox with a weight up to 1.6 kg and wingspan up to 1.7 m.

 

CLASSIFICATION AND EVOLUTION

Bats are mammals. In many languages, the word for "bat" is cognate with the word for "mouse": for example, chauve-souris ("bald-mouse") in French, murciélago ("blind mouse") in Spanish, saguzahar ("old mouse") in Basque, летучая мышь ("flying mouse") in Russian, slijepi miš ("blind mouse") in Bosnian, nahkhiir ("leather mouse") in Estonian, vlermuis (winged mouse) in Afrikaans, from the Dutch word vleermuis (from Middle Dutch "winged mouse"). An older English name for bats is flittermouse, which matches their name in other Germanic languages (for example German Fledermaus and Swedish fladdermus). Bats were formerly thought to have been most closely related to the flying lemurs, treeshrews, and primates, but recent molecular cladistics research indicates that they actually belong to Laurasiatheria, a diverse group also containing Carnivora and Artiodactyla.

 

The two traditionally recognized suborders of bats are:

 

- Megachiroptera (megabats)

- Microchiroptera (microbats/echolocating bats)

 

Not all megabats are larger than microbats. The major distinctions between the two suborders are:

 

- Microbats use echolocation; with the exception of the Rousettus genus, megabats do not.

- Microbats lack the claw at the second finger of the forelimb.

- The ears of microbats do not close to form a ring; the edges are separated from each other at the base of the ear.

- Microbats lack underfur; they are either naked or have guard hairs.

 

Megabats eat fruit, nectar, or pollen. Most microbats eat insects; others may feed on fruit, nectar, pollen, fish, frogs, small mammals, or the blood of animals. Megabats have well-developed visual cortices and show good visual acuity, while microbats rely on echolocation for navigation and finding prey.

 

The phylogenetic relationships of the different groups of bats have been the subject of much debate. The traditional subdivision between Megachiroptera and Microchiroptera reflects the view that these groups of bats have evolved independently of each other for a long time, from a common ancestor already capable of flight. This hypothesis recognized differences between microbats and megabats and acknowledged that flight has only evolved once in mammals. Most molecular biological evidence supports the view that bats form a single or monophyletic group.

 

Researchers have proposed alternative views of chiropteran phylogeny and classification, but more research is needed.

 

In the 1980s, a hypothesis based on morphological evidence was offered that stated the Megachiroptera evolved flight separately from the Microchiroptera. The so-called flying primates theory proposes that, when adaptations to flight are removed, the Megachiroptera are allied to primates by anatomical features not shared with Microchiroptera. One example is that the brains of megabats show a number of advanced characteristics that link them to primates. Although recent genetic studies strongly support the monophyly of bats, debate continues as to the meaning of available genetic and morphological evidence.

 

Genetic evidence indicates that megabats originated during the early Eocene and should be placed within the four major lines of microbats.

 

Consequently, two new suborders based on molecular data have been proposed. The new suborder of Yinpterochiroptera includes the Pteropodidae, or megabat family, as well as the Rhinolophidae, Hipposideridae, Craseonycteridae, Megadermatidae, and Rhinopomatidae families The other new suborder, Yangochiroptera, includes all of the remaining families of bats (all of which use laryngeal echolocation). These two new suborders are strongly supported by statistical tests. Teeling (2005) found 100% bootstrap support in all maximum likelihood analyses for the division of Chiroptera into these two modified suborders. This conclusion is further supported by a 15-base-pair deletion in BRCA1 and a seven-base-pair deletion in PLCB4 present in all Yangochiroptera and absent in all Yinpterochiroptera. Perhaps most convincingly, a phylogenomic study by Tsagkogeorga et al (2013) showed that the two new proposed suborders were supported by analyses of thousands of genes.

 

The chiropteran phylogeny based on molecular evidence is controversial because microbat paraphyly implies that one of two seemingly unlikely hypotheses occurred. The first suggests that laryngeal echolocation evolved twice in Chiroptera, once in Yangochiroptera and once in the rhinolophoids. The second proposes that laryngeal echolocation had a single origin in Chiroptera, was subsequently lost in the family Pteropodidae (all megabats), and later evolved as a system of tongue-clicking in the genus Rousettus.

 

Analyses of the sequence of the "vocalization" gene, FoxP2, were inconclusive as to whether laryngeal echolocation was secondarily lost in the pteropodids or independently gained in the echolocating lineages. However, analyses of the "hearing" gene, Prestin seemed to favor the independent gain in echolocating species rather than a secondary loss in the pteropodids.

 

In addition to Yinpterochiroptera and Yangochiroptera, the names Pteropodiformes and Vespertilioniformes have also been proposed for these suborders. Under this new proposed nomenclature, the suborder Pteropodiformes includes all extant bat families more closely related to the genus Pteropus than the genus Vespertilio, while the suborder Vespertilioniformes includes all extant bat families more closely related to the genus Vespertilio than to the genus Pteropus.

 

Little fossil evidence is available to help map the evolution of bats, since their small, delicate skeletons do not fossilize very well. However, a Late Cretaceous tooth from South America resembles that of an early microchiropteran bat. Most of the oldest known, definitely identified bat fossils were already very similar to modern microbats. These fossils, Icaronycteris, Archaeonycteris, Palaeochiropteryx and Hassianycteris, are from the early Eocene period, 52.5 million years ago. Archaeopteropus, formerly classified as the earliest known megachiropteran, is now classified as a microchiropteran.

 

Bats were formerly grouped in the superorder Archonta, along with the treeshrews (Scandentia), colugos (Dermoptera), and the primates, because of the apparent similarities between Megachiroptera and such mammals. Genetic studies have now placed bats in the superorder Laurasiatheria, along with carnivorans, pangolins, odd-toed ungulates, even-toed ungulates, and cetaceans. A recent study by Zhang et al. places Chiroptera as a sister taxon to the clade Perissodactyla (which includes horses and other odd-toed ungulates). However, the first phylogenomic analysis of bats shows that they are not sisters to Perissodactyla, instead they are sisters to a larger group that includes ungulates and carnivores.

 

Megabats primarily eat fruit or nectar. In New Guinea, they are likely to have evolved for some time in the absence of microbats, which has resulted in some smaller megabats of the genus Nyctimene becoming (partly) insectivorous to fill the vacant microbat ecological niche. Furthermore, some evidence indicates that the fruit bat genus Pteralopex from the Solomon Islands, and its close relative Mirimiri from Fiji, have evolved to fill some niches that were open because there are no nonvolant or nonflying mammals on those islands.

 

FOSSIL BATS

Fossilized remains of bats are few, as they are terrestrial and light-boned. Only an estimated 12% of the bat fossil record is complete at the genus level. Fossil remains of an Eocene bat, Icaronycteris, were found in 1960. Another Eocene bat, Onychonycteris finneyi, was found in the 52-million-year-old Green River Formation in Wyoming, United States, in 2003. This intermediate fossil has helped to resolve a long-standing disagreement regarding whether flight or echolocation developed first in bats. The shape of the rib cage, faceted infraspious fossa of the scapula, manus morphology, robust clavicle, and keeled sternum all indicated Onychonycteris was capable of powered flight. However, the well-preserved skeleton showed that the small cochlea of the inner ear did not have the morphology necessary to echolocate. O. finneyi lacked an enlarged orbical apophysis on the malleus, and a stylohyal element with an expanded paddle-like cranial tip - both of which are characteristics linked to echolocation in other prehistoric and extant bat species. Because of these absences, and the presence of characteristics necessary for flight, Onychonycteris provides strong support for the “flight first” hypothesis in the evolution of flight and echolocation in bats.

 

The appearance and flight movement of bats 52.5 million years ago were different from those of bats today. Onychonycteris had claws on all five of its fingers, whereas modern bats have at most two claws appearing on two digits of each hand. It also had longer hind legs and shorter forearms, similar to climbing mammals that hang under branches such as sloths and gibbons. This palm-sized bat had short, broad wings, suggesting it could not fly as fast or as far as later bat species. Instead of flapping its wings continuously while flying, Onychonycteris likely alternated between flaps and glides while in the air. Such physical characteristics suggest that this bat did not fly as much as modern bats do, rather flying from tree to tree and spending most of its waking day climbing or hanging on the branches of trees. The distinctive features noted on the Onychonycteris fossil also support the claim that mammalian flight most likely evolved in arboreal gliders, rather than terrestrial runners. This model of flight development, commonly known as the "trees-down" theory, implies that bats attained powered flight by taking advantage of height and gravity, rather than relying on running speeds fast enough for a ground-level take off.

 

The mid-Eocene genus Necromantis is one of the earliest examples of bats specialised to hunt vertebrate prey, as well as one of the largest bats of its epoch.

 

HABITATS

Flight has enabled bats to become one of the most widely distributed groups of mammals. Apart from the Arctic, the Antarctic and a few isolated oceanic islands, bats exist all over the world. Bats are found in almost every habitat available on Earth. Different species select different habitats during different seasons, ranging from seasides to mountains and even deserts, but bat habitats have two basic requirements: roosts, where they spend the day or hibernate, and places for foraging. Most temperate species additionally need a relatively warm hibernation shelter. Bat roosts can be found in hollows, crevices, foliage, and even human-made structures, and include "tents" the bats construct by biting leaves.

 

The United States is home to an estimated 45 to 48 species of bats. The three most common species are Myotis lucifugus (little brown bat), Eptesicus fuscus (big brown bat), and Tadarida brasiliensis (Mexican free-tailed bat). The little and the big brown bats are common throughout the northern two-thirds of the country, while the Mexican free-tailed bat is the most common species in the southwest, sometimes even appearing in portions of the Southeast.

 

ANATOMY

WINGS

The finger bones of bats are much more flexible than those of other mammals, owing to their flattened cross-section and to low levels of minerals, such as calcium, near their tips. In 2006, Sears et al. published a study that traces the elongation of manual bat digits, a key feature required for wing development, to the upregulation of bone morphogenetic proteins (Bmps). During embryonic development, the gene controlling Bmp signaling, Bmp2, is subjected to increased expression in bat forelimbs - resulting in the extension of the offspring's manual digits. This crucial genetic alteration helps create the specialized limbs required for volant locomotion. Sears et al. (2006) also studied the relative proportion of bat forelimb digits from several extant species and compared these with a fossil of Lcaronycteris index, an early extinct species from approximately 50 million years ago. The study found no significant differences in relative digit proportion, suggesting that bat wing morphology has been conserved for over 50 million years.The wings of bats are much thinner and consist of more bones than the wings of birds, allowing bats to maneuver more accurately than the latter, and fly with more lift and less drag. By folding the wings in toward their bodies on the upstroke, they save 35 percent energy during flight. The membranes are also delicate, ripping easily; however, the tissue of the bat's membrane is able to regrow, such that small tears can heal quickly. The surface of their wings is equipped with touch-sensitive receptors on small bumps called Merkel cells, also found on human fingertips. These sensitive areas are different in bats, as each bump has a tiny hair in the center, making it even more sensitive and allowing the bat to detect and collect information about the air flowing over its wings, and to fly more efficiently by changing the shape of its wings in response. An additional kind of receptor cell is found in the wing membrane of species that use their wings to catch prey. This receptor cell is sensitive to the stretching of the membrane. The cells are concentrated in areas of the membrane where insects hit the wings when the bats capture them.

 

OTHER

The teeth of microbats resemble insectivorans. They are very sharp to bite through the hardened armor of insects or the skin of fruit.

 

Mammals have one-way valves in their veins to prevent the blood from flowing backwards, but bats also have one-way valves in their arteries.

 

The tube-lipped nectar bat (Anoura fistulata) has the longest tongue of any mammal relative to its body size. This is beneficial to them in terms of pollination and feeding. Their long, narrow tongues can reach deep into the long cup shape of some flowers. When the tongue retracts, it coils up inside its rib cage.

 

Bats possess highly adapted lung systems to cope with the pressures of powered-flight. Flight is an energetically taxing aerobic activity and requires large amounts of oxygen to be sustained. In bats, the relative alveolar surface area and pulmonary capillary blood volume are significantly larger than most other small quadrupedal mammals.

 

ECHOLOCATION

Bat echolocation is a perceptual system where ultrasonic sounds are emitted specifically to produce echoes. By comparing the outgoing pulse with the returning echoes, the brain and auditory nervous system can produce detailed images of the bat's surroundings. This allows bats to detect, localize, and even classify their prey in complete darkness. At 130 decibels in intensity, bat calls are some of the most intense, airborne animal sounds.

 

To clearly distinguish returning information, bats must be able to separate their calls from the echoes that they receive. Microbats use two distinct approaches.

 

Low duty cycle echolocation: Bats can separate their calls and returning echoes by time. Bats that use this approach time their short calls to finish before echoes return. This is important because these bats contract their middle ear muscles when emitting a call, so they can avoid deafening themselves. The time interval between the call and echo allows them to relax these muscles, so they can clearly hear the returning echo. The delay of the returning echoes provides the bat with the ability to estimate the range to their prey.

 

High duty cycle echolocation: Bats emit a continuous call and separate pulse and echo in frequency. The ears of these bats are sharply tuned to a specific frequency range. They emit calls outside of this range to avoid self-deafening. They then receive echoes back at the finely tuned frequency range by taking advantage of the Doppler shift of their motion in flight. The Doppler shift of the returning echoes yields information relating to the motion and location of the bat's prey. These bats must deal with changes in the Doppler shift due to changes in their flight speed. They have adapted to change their pulse emission frequency in relation to their flight speed so echoes still return in the optimal hearing range.

 

The new Yinpterochiroptera and Yangochiroptera classification of bats, supported by molecular evidence, suggests two possibilities for the evolution of echolocation. It may have been gained once in a common ancestor of all bats and was then subsequently lost in the Old World fruit bats, only to be regained in the horseshoe bats, or echolocation evolved independently in both the Yinpterochiroptera and Yangochiroptera lineages.

 

Two groups of moths exploit a bat sense to echolocate: tiger moths produce ultrasonic signals to warn the bats that they (the moths) are chemically protected or aposematic, other moth species produce signals to jam bat echolocation. Many moth species have a hearing organ called a tympanum, which responds to an incoming bat signal by causing the moth's flight muscles to twitch erratically, sending the moth into random evasive maneuvers.

 

In addition to echolocating prey, bat ears are sensitive to the fluttering of moth wings, the sounds produced by tymbalate insects, and the movement of ground-dwelling prey, such as centipedes, earwigs, etc. The complex geometry of ridges on the inner surface of bat ears helps to sharply focus not only echolocation signals, but also to passively listen for any other sound produced by the prey. These ridges can be regarded as the acoustic equivalent of a Fresnel lens, and may be seen in a large variety of unrelated animals, such as the aye-aye, lesser galago, bat-eared fox, mouse lemur, and others.

 

By repeated scanning, bats can mentally construct an accurate image of the environment in which they are moving and of their prey item.

 

OTHER SENSES

Although the eyes of most microbat species are small and poorly developed, leading to poor visual acuity, no species is blind. Microbats use vision to navigate, especially for long distances when beyond the range of echolocation, and species that are gleaners - that is, ones that attempt to swoop down from above to ambush tasty insects like crickets on the ground or moths up a tree - often have eyesight about as good as a rat's. Some species have been shown to be able to detect ultraviolet light, and most cave dwelling species have developed the ability to utilize very dim light. They also have high-quality senses of smell and hearing. Bats hunt at night, reducing competition with birds, minimizing contact with certain predators, and travel large distances (up to 800 km) in their search for food. Megabat species often have excellent eyesight as good as, if not better than, human vision; they need this for the warm climates they live in and the very social world they occupy, where relations and friends need to be distinguished from other bats in the colony. This eyesight is, unlike its microbat relations, adapted to both night and daylight vision and enables the bat to have some colour vision whereas the microbat sees in blurred shades of grey.

 

BEHAVIOUR

Most microbats are nocturnal and are active at twilight. A large portion of bats migrate hundreds of kilometres to winter hibernation dens, while some pass into torpor in cold weather, rousing and feeding when warm weather allows for insects to be active. Others retreat to caves for winter and hibernate for six months. Bats rarely fly in rain, as the rain interferes with their echolocation, and they are unable to locate their food.

 

The social structure of bats varies, with some leading solitary lives and others living in caves colonized by more than a million bats. The fission-fusion social structure is seen among several species of bats. The term "fusion" refers to a large numbers of bats that congregate in one roosting area, and "fission" refers to breaking up and the mixing of subgroups, with individual bats switching roosts with others and often ending up in different trees and with different roostmates.

 

Studies also show that bats make all kinds of sounds to communicate with others. Scientists in the field have listened to bats and have been able to associate certain sounds with certain behaviours that bats make after the sounds are made.

 

Insectivores make up 70% of bat species and locate their prey by means of echolocation. Of the remainder, most feed on fruits. Only three species sustain themselves with blood.

 

Some species even prey on vertebrates. The leaf-nosed bats (Phyllostomidae) of Central America and South America, and the two bulldog bat (Noctilionidae) species feed on fish. At least two species of bat are known to feed on other bats: the spectral bat, also known as the American false vampire bat, and the ghost bat of Australia. One species, the greater noctule bat, catches and eats small birds in the air.

 

Predators of bats include bat hawks, bat falcons and even spiders.

 

REPRODUCTION

Most bats have a breeding season, which is in the spring for species living in a temperate climate. Bats may have one to three litters in a season, depending on the species and on environmental conditions, such as the availability of food and roost sites. Females generally have one offspring at a time, which could be a result of the mother's need to fly to feed while pregnant. Female bats nurse their young until they are nearly adult size, because a young bat cannot forage on its own until its wings are fully developed.

 

Female bats use a variety of strategies to control the timing of pregnancy and the birth of young, to make delivery coincide with maximum food ability and other ecological factors. Females of some species have delayed fertilization, in which sperm is stored in the reproductive tract for several months after mating. In many such cases, mating occurs in the fall, and fertilization does not occur until the following spring. Other species exhibit delayed implantation, in which the egg is fertilized after mating, but remains free in the reproductive tract until external conditions become favorable for giving birth and caring for the offspring.

 

In yet another strategy, fertilization and implantation both occur, but development of the fetus is delayed until favorable conditions prevail, during the delayed development the mother still gives the fertilized egg nutrients, and oxygenated blood to keep it alive. However, this process can go for a long period of time, because of the advanced gas exchange system. All of these adaptations result in the pup being born during a time of high local production of fruit or insects.

 

At birth, the wings are too small to be used for flight. Young microbats become independent at the age of six to eight weeks, while megabats do not until they are four months old.

 

LIFE EXPECTANCY

A single bat can live over 20 years, but bat population growth is limited by the slow birth rate.

 

HUNTING, FEEDING AND DRINKING

Newborn bats rely on the milk from their mothers. When they are a few weeks old, bats are expected to fly and hunt on their own. It is up to them to find and catch their prey, along with satisfying their thirst.

 

HUNTING

Most bats are nocturnal creatures. Their daylight hours are spent grooming and sleeping; they hunt during the night. The means by which bats navigate while finding and catching their prey in the dark was unknown until the 1790s, when Lazzaro Spallanzani conducted a series of experiments on a group of blind bats. These bats were placed in a room in total darkness, with silk threads strung across the room. Even then, the bats were able to navigate their way through the room. Spallanzani concluded the bats were not using their eyes to fly through complete darkness, but something else.

 

Spallanzani decided the bats were able to catch and find their prey through the use of their ears. To prove this theory, Spallanzani plugged the ears of the bats in his experiment. To his pleasure, he found that the bats with plugged ears were not able to fly with the same amount of skill and precision as they were able to without their ears plugged. Unfortunately for Spallanzani, the twin concepts of sound waves and acoustics would not be understood for another century and he could not explain why specifically the bats were crashing into walls and the threads that he'd strung up around the room, and because of the methodology Spallanzani used, many of his test subjects died.

 

It was thus well known through the nineteenth century that the chiropteran ability to navigate had something to do with hearing, but how they accomplish this was not proven conclusively until the 1930s, by Donald R. Griffin, a biology student at Harvard University. Using a locally native species, the little brown bat, he discovered that bats use echolocation to locate and catch their prey. When bats fly, they produce a constant stream of high-pitched sounds. When the sound waves produced by these sounds hit an insect or other animal, the echoes bounce back to the bat, and guide them to the source.

 

FEEDING AND DIET

The majority of food consumed by bats includes insects, fruits and flower nectar, vertebrates and blood. Almost three-fourths of the world's bats are insect eaters. Bats consume both aerial and ground-dwelling insects. Each bat is typically able to consume one-third of its body weight in insects each night, and several hundred insects in a few hours. This means that a group of a thousand bats could eat four tons of insects each year. If bats were to become extinct, it has been calculated that the insect population would reach an alarmingly high number.

 

VITAMIN C

In a test of 34 bat species from six major families of bats, including major insect- and fruit-eating bat families, all were found to have lost the ability to synthesize vitamin C, and this loss may derive from a common bat ancestor, as a single mutation. However, recent results show that there are at least two species of bat, the frugivorous bat (Rousettus leschenaultii) and insectivorous bat (Hipposideros armiger), that have retained their ability to produce vitamin C. In fact, the whole Chiroptera are in the process of losing the ability to synthesize Vc which most of them have already lost.

 

AERIAL INSECTIVORES

Watching a bat catch and eat an insect is difficult. The action is so fast that all one sees is a bat rapidly change directions, and continue on its way. Scientist Frederick A. Webster discovered how bats catch their prey. In 1960, Webster developed a high-speed camera that was able to take one thousand pictures per second. These photos revealed the fast and precise way in which bats catch insects. Occasionally, a bat will catch an insect in mid-air with its mouth, and eat it in the air. However, more often than not, a bat will use its tail membrane or wings to scoop up the insect and trap it in a sort of "bug net". Then, the bat will take the insect back to its roost. There, the bat will proceed to eat said insect, often using its tail membrane as a kind of napkin, to prevent its meal from falling to the ground. One common insect prey is Helicoverpa zea, a moth that causes major agricultural damage.

 

FORAGE GLEANERS

These bats typically fly down and grasp their prey off the ground with their teeth, and take it to a nearby perch to eat it. Generally, these bats do not use echolocation to locate their prey. Instead, they rely on the sounds produced by the insects. Some make unique sounds, and almost all make some noise while moving through the environment.

 

FRUITS AND FLOWER NECTAR

Fruit eating, or frugivory, is a specific habit found in two families of bats. Megachiropterans and microchiropterans both include species of bat that feed on fruits. These bats feed on the juices of sweet fruits, and fulfill the needs of some seeds to be dispersed. The fruits preferred by most fruit-eating bats are fleshy and sweet, but not particularly strong smelling or colorful. To get the juice of these fruits, bats pull the fruit off the trees with their teeth, and fly back to their roosts with the fruit in their mouths. There, the bats will consume the fruit in a specific way. To do this, the bats crush open the fruit and eat the parts that satisfy their hunger. The remainder of the fruit, the seeds and pulp, are spat onto the ground. These seeds take root and begin to grow into new fruit trees. Over 150 types of plants depend on bats in order to reproduce.Some bats prefer the nectar of flowers to insects or other animals. These bats have evolved specifically for this purpose. For example, these bats possess long muzzles and long, extensible tongues covered in fine bristles that aid them in feeding on particular flowers and plants.[68] When they sip the nectar from these flowers, pollen gets stuck to their fur, and is dusted off when the bats take flight, thus pollinating the plants below them. The rainforest is said to be the most benefitted of all the biomes where bats live, because of the large variety of appealing plants. Because of their specific eating habits, nectar-feeding bats are more prone to extinction than any other type of bat. However, bats benefit from eating fruits and nectar just as much as from eating insects.

 

VERTEBRATES

A small group of carnivorous bats feed on other vertebrates and are considered the top carnivores of the bat world. These bats typically eat a variety of animals, but normally consume frogs, lizards, birds, and sometimes other bats. For example, one vertebrate predator, Trachops cirrhosus, is particularly skilled at catching frogs. These bats locate large groups of frogs by distinguishing their mating calls from other sounds around them. They follow the sounds to the source and pluck them from the surface of the water with their sharp canine teeth. Another example is the greater noctule bat, which is believed to catch birds on the wing.

 

Also, several species of bat feed on fish. These types of bats are found on almost all continents. They use echolocation to detect tiny ripples in the water's surface to locate fish. From there, the bats swoop down low, inches from the water, and use specially enlarged claws on their hind feet to grab the fish out of the water. The bats then take the fish to a feeding roost and consume the animal.

 

BLOOD

A few species of bats exclusively consume blood as their diet. This type of diet is referred to as hematophagy, and three species of bats exhibit this behavior. These species are the common, the white-winged, and the hairy-legged vampire bats. The common vampire bat typically consumes the blood of mammals, while the hairy-legged and white-winged vampires feed on the blood of birds. These species live only in Mexico, Central, and South America, with a presence also on the Island of Trinidad.

 

DEFECATION

Bat dung, or guano, is so rich in nutrients that it is mined from caves, bagged, and used by farmers to fertilize their crops. During the U.S. Civil War, guano was used to make gunpowder.

 

To survive hibernation months, some species build up large reserves of body fat, both as fuel and as insulation.

 

DRINKING

In 1960, Frederic A. Webster discovered bats' method of drinking water using a high-speed camera and flashgun that could take 1,000 photos per second. Webster's camera captured a bat skimming the surface of a body of water, and lowering its jaw to get just one drop of water. It then skimmed again to get a second drop of water, and so on, until it has had its fill. A bat's precision and control during flight is very fine, and it almost never misses. Other bats, such as the flying fox or fruit bat, gently skim the water's surface, then land nearby to lick water from chest fur.

 

WIKIPEDIA

ANDAMAN SEA (Dec. 13, 2021) A twin boom extensible crane (TBEC) traverses an 11-meter rigid-hull inflatable boat (RHIB) to the mission bay during boat operations aboard Independence-variant littoral combat ship USS Tulsa (LCS 16). Tulsa, part of Destroyer Squadron (DESRON) 7, is on a rotational deployment, operating in U.S. 7th Fleet to enhance interoperability with partners and serve as a ready-response force in support of a free and open Indo-Pacific region. (U.S. Navy photo by Mass Communication Specialist 1st Class Devin M. Langer)

Jellyfish, also known sea jellies, are the medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria.

 

Jellyfish are mainly free-swimming marine animals with umbrella-shaped bells and trailing tentacles, although a few are anchored to the seabed by stalks rather than being mobile. The bell can pulsate to provide propulsion for highly efficient locomotion. The tentacles are armed with stinging cells and may be used to capture prey and defend against predators. Jellyfish have a complex life cycle. The medusa is normally the sexual phase, which produces planula larvae; these then disperse widely and enter a sedentary polyp phase, before reaching sexual maturity.

 

Jellyfish are found all over the world, from surface waters to the deep sea. Scyphozoans (the "true jellyfish") are exclusively marine, but some hydrozoans with a similar appearance live in freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide. The medusae of most species are fast-growing, and mature within a few months then die soon after breeding, but the polyp stage, attached to the seabed, may be much more long-lived. Jellyfish have been in existence for at least 500 million years, and possibly 700 million years or more, making them the oldest multi-organ animal group.

 

Jellyfish are eaten by humans in certain cultures. They are considered a delicacy in some Asian countries, where species in the Rhizostomeae order are pressed and salted to remove excess water. Australian researchers have described them as a "perfect food": sustainable and protein-rich but relatively low in food energy.

 

They are also used in research, where the green fluorescent protein used by some species to cause bioluminescence has been adapted as a fluorescent marker for genes inserted into other cells or organisms.

 

The stinging cells used by jellyfish to subdue their prey can injure humans. Thousands of swimmers worldwide are stung every year, with effects ranging from mild discomfort to serious injury or even death. When conditions are favourable, jellyfish can form vast swarms, which can be responsible for damage to fishing gear by filling fishing nets, and sometimes clog the cooling systems of power and desalination plants which draw their water from the sea.

  

Names

The name jellyfish, in use since 1796, has traditionally been applied to medusae and all similar animals including the comb jellies (ctenophores, another phylum). The term jellies or sea jellies is more recent, having been introduced by public aquaria in an effort to avoid use of the word "fish" with its modern connotation of an animal with a backbone, though shellfish, cuttlefish and starfish are not vertebrates either. In scientific literature, "jelly" and "jellyfish" have been used interchangeably. Many sources refer to only scyphozoans as "true jellyfish".

 

A group of jellyfish is called a "smack" or a "smuck".

 

Definition

The term jellyfish broadly corresponds to medusae, that is, a life-cycle stage in the Medusozoa. The American evolutionary biologist Paulyn Cartwright gives the following general definition:

 

Typically, medusozoan cnidarians have a pelagic, predatory jellyfish stage in their life cycle; staurozoans are the exceptions [as they are stalked].

 

The Merriam-Webster dictionary defines jellyfish as follows:

 

A free-swimming marine coelenterate that is the sexually reproducing form of a hydrozoan or scyphozoan and has a nearly transparent saucer-shaped body and extensible marginal tentacles studded with stinging cells.

 

Given that jellyfish is a common name, its mapping to biological groups is inexact. Some authorities have called the comb jellies and certain salps jellyfish, though other authorities state that neither of these are jellyfish, which they consider should be limited to certain groups within the medusozoa.

 

The non-medusozoan clades called jellyfish by some but not all authorities (both agreeing and disagreeing citations are given in each case) are indicated with on the following cladogram of the animal kingdom:

 

Jellyfish are not a clade, as they include most of the Medusozoa, barring some of the Hydrozoa. The medusozoan groups included by authorities are indicated on the following phylogenetic tree by the presence of citations. Names of included jellyfish, in English where possible, are shown in boldface; the presence of a named and cited example indicates that at least that species within its group has been called a jellyfish.

 

Taxonomy

The subphylum Medusozoa includes all cnidarians with a medusa stage in their life cycle. The basic cycle is egg, planula larva, polyp, medusa, with the medusa being the sexual stage. The polyp stage is sometimes secondarily lost. The subphylum include the major taxa, Scyphozoa (large jellyfish), Cubozoa (box jellyfish) and Hydrozoa (small jellyfish), and excludes Anthozoa (corals and sea anemones). This suggests that the medusa form evolved after the polyps. Medusozoans have tetramerous symmetry, with parts in fours or multiples of four.

 

The four major classes of medusozoan Cnidaria are:

Scyphozoa are sometimes called true jellyfish, though they are no more truly jellyfish than the others listed here. They have tetra-radial symmetry. Most have tentacles around the outer margin of the bowl-shaped bell, and long, oral arms around the mouth in the center of the subumbrella.

Cubozoa (box jellyfish) have a (rounded) box-shaped bell, and their velarium assists them to swim more quickly. Box jellyfish may be related more closely to scyphozoan jellyfish than either are to the Hydrozoa.

Hydrozoa medusae also have tetra-radial symmetry, nearly always have a velum (diaphragm used in swimming) attached just inside the bell margin, do not have oral arms, but a much smaller central stalk-like structure, the manubrium, with terminal mouth opening, and are distinguished by the absence of cells in the mesoglea. Hydrozoa show great diversity of lifestyle; some species maintain the polyp form for their entire life and do not form medusae at all (such as Hydra, which is hence not considered a jellyfish), and a few are entirely medusal and have no polyp form.

Staurozoa (stalked jellyfish) are characterized by a medusa form that is generally sessile, oriented upside down and with a stalk emerging from the apex of the "calyx" (bell), which attaches to the substrate. At least some Staurozoa also have a polyp form that alternates with the medusoid portion of the life cycle. Until recently, Staurozoa were classified within the Scyphozoa.

There are over 200 species of Scyphozoa, about 50 species of Staurozoa, about 50 species of Cubozoa, and the Hydrozoa includes about 1000–1500 species that produce medusae, but many more species that do not.

 

Fossil history

Since jellyfish have no hard parts, fossils are rare. The oldest unambiguous fossil of a free-swimming medusa is Burgessomedusa from the mid Cambrian Burgess Shale of Canada, which is likely either a stem group of box jellyfish (Cubozoa) or Acraspeda (the clade including Staurozoa, Cubozoa, and Scyphozoa). Other claimed records from the Cambrian of China and Utah in the United States are uncertain, and possibly represent ctenophores instead.

 

Anatomy

The main feature of a true jellyfish is the umbrella-shaped bell. This is a hollow structure consisting of a mass of transparent jelly-like matter known as mesoglea, which forms the hydrostatic skeleton of the animal. 95% or more of the mesogloea consists of water, but it also contains collagen and other fibrous proteins, as well as wandering amoebocytes which can engulf debris and bacteria. The mesogloea is bordered by the epidermis on the outside and the gastrodermis on the inside. The edge of the bell is often divided into rounded lobes known as lappets, which allow the bell to flex. In the gaps or niches between the lappets are dangling rudimentary sense organs known as rhopalia, and the margin of the bell often bears tentacles.

  

Anatomy of a scyphozoan jellyfish

On the underside of the bell is the manubrium, a stalk-like structure hanging down from the centre, with the mouth, which also functions as the anus, at its tip. There are often four oral arms connected to the manubrium, streaming away into the water below. The mouth opens into the gastrovascular cavity, where digestion takes place and nutrients are absorbed. This is subdivided by four thick septa into a central stomach and four gastric pockets. The four pairs of gonads are attached to the septa, and close to them four septal funnels open to the exterior, perhaps supplying good oxygenation to the gonads. Near the free edges of the septa, gastric filaments extend into the gastric cavity; these are armed with nematocysts and enzyme-producing cells and play a role in subduing and digesting the prey. In some scyphozoans, the gastric cavity is joined to radial canals which branch extensively and may join a marginal ring canal. Cilia in these canals circulate the fluid in a regular direction.

  

Discharge mechanism of a nematocyst

The box jellyfish is largely similar in structure. It has a squarish, box-like bell. A short pedalium or stalk hangs from each of the four lower corners. One or more long, slender tentacles are attached to each pedalium. The rim of the bell is folded inwards to form a shelf known as a velarium which restricts the bell's aperture and creates a powerful jet when the bell pulsates, allowing box jellyfish to swim faster than true jellyfish. Hydrozoans are also similar, usually with just four tentacles at the edge of the bell, although many hydrozoans are colonial and may not have a free-living medusal stage. In some species, a non-detachable bud known as a gonophore is formed that contains a gonad but is missing many other medusal features such as tentacles and rhopalia. Stalked jellyfish are attached to a solid surface by a basal disk, and resemble a polyp, the oral end of which has partially developed into a medusa with tentacle-bearing lobes and a central manubrium with four-sided mouth.

 

Most jellyfish do not have specialized systems for osmoregulation, respiration and circulation, and do not have a central nervous system. Nematocysts, which deliver the sting, are located mostly on the tentacles; true jellyfish also have them around the mouth and stomach. Jellyfish do not need a respiratory system because sufficient oxygen diffuses through the epidermis. They have limited control over their movement, but can navigate with the pulsations of the bell-like body; some species are active swimmers most of the time, while others largely drift. The rhopalia contain rudimentary sense organs which are able to detect light, water-borne vibrations, odour and orientation. A loose network of nerves called a "nerve net" is located in the epidermis. Although traditionally thought not to have a central nervous system, nerve net concentration and ganglion-like structures could be considered to constitute one in most species. A jellyfish detects stimuli, and transmits impulses both throughout the nerve net and around a circular nerve ring, to other nerve cells. The rhopalial ganglia contain pacemaker neurones which control swimming rate and direction.

 

In many species of jellyfish, the rhopalia include ocelli, light-sensitive organs able to tell light from dark. These are generally pigment spot ocelli, which have some of their cells pigmented. The rhopalia are suspended on stalks with heavy crystals at one end, acting like gyroscopes to orient the eyes skyward. Certain jellyfish look upward at the mangrove canopy while making a daily migration from mangrove swamps into the open lagoon, where they feed, and back again.

 

Box jellyfish have more advanced vision than the other groups. Each individual has 24 eyes, two of which are capable of seeing colour, and four parallel information processing areas that act in competition, supposedly making them one of the few kinds of animal to have a 360-degree view of its environment.

 

Box jellyfish eye

The study of jellyfish eye evolution is an intermediary to a better understanding of how visual systems evolved on Earth. Jellyfish exhibit immense variation in visual systems ranging from photoreceptive cell patches seen in simple photoreceptive systems to more derived complex eyes seen in box jellyfish. Major topics of jellyfish visual system research (with an emphasis on box jellyfish) include: the evolution of jellyfish vision from simple to complex visual systems), the eye morphology and molecular structures of box jellyfish (including comparisons to vertebrate eyes), and various uses of vision including task-guided behaviors and niche specialization.

 

Evolution

Experimental evidence for photosensitivity and photoreception in cnidarians antecedes the mid 1900s, and a rich body of research has since covered evolution of visual systems in jellyfish. Jellyfish visual systems range from simple photoreceptive cells to complex image-forming eyes. More ancestral visual systems incorporate extraocular vision (vision without eyes) that encompass numerous receptors dedicated to single-function behaviors. More derived visual systems comprise perception that is capable of multiple task-guided behaviors.

 

Although they lack a true brain, cnidarian jellyfish have a "ring" nervous system that plays a significant role in motor and sensory activity. This net of nerves is responsible for muscle contraction and movement and culminates the emergence of photosensitive structures. Across Cnidaria, there is large variation in the systems that underlie photosensitivity. Photosensitive structures range from non-specialized groups of cells, to more "conventional" eyes similar to those of vertebrates. The general evolutionary steps to develop complex vision include (from more ancestral to more derived states): non-directional photoreception, directional photoreception, low-resolution vision, and high-resolution vision. Increased habitat and task complexity has favored the high-resolution visual systems common in derived cnidarians such as box jellyfish.

 

Basal visual systems observed in various cnidarians exhibit photosensitivity representative of a single task or behavior. Extraocular photoreception (a form of non-directional photoreception), is the most basic form of light sensitivity and guides a variety of behaviors among cnidarians. It can function to regulate circadian rhythm (as seen in eyeless hydrozoans) and other light-guided behaviors responsive to the intensity and spectrum of light. Extraocular photoreception can function additionally in positive phototaxis (in planula larvae of hydrozoans), as well as in avoiding harmful amounts of UV radiation via negative phototaxis. Directional photoreception (the ability to perceive direction of incoming light) allows for more complex phototactic responses to light, and likely evolved by means of membrane stacking. The resulting behavioral responses can range from guided spawning events timed by moonlight to shadow responses for potential predator avoidance. Light-guided behaviors are observed in numerous scyphozoans including the common moon jelly, Aurelia aurita, which migrates in response to changes in ambient light and solar position even though they lack proper eyes.

 

The low-resolution visual system of box jellyfish is more derived than directional photoreception, and thus box jellyfish vision represents the most basic form of true vision in which multiple directional photoreceptors combine to create the first imaging and spatial resolution. This is different from the high-resolution vision that is observed in camera or compound eyes of vertebrates and cephalopods that rely on focusing optics. Critically, the visual systems of box jellyfish are responsible for guiding multiple tasks or behaviors in contrast to less derived visual systems in other jellyfish that guide single behavioral functions. These behaviors include phototaxis based on sunlight (positive) or shadows (negative), obstacle avoidance, and control of swim-pulse rate.

 

Box jellyfish possess "proper eyes" (similar to vertebrates) that allow them to inhabit environments that lesser derived medusae cannot. In fact, they are considered the only class in the clade Medusozoa that have behaviors necessitating spatial resolution and genuine vision. However, the lens in their eyes are more functionally similar to cup-eyes exhibited in low-resolution organisms, and have very little to no focusing capability. The lack of the ability to focus is due to the focal length exceeding the distance to the retina, thus generating unfocused images and limiting spatial resolution. The visual system is still sufficient for box jellyfish to produce an image to help with tasks such as object avoidance.

 

Utility as a model organism

Box jellyfish eyes are a visual system that is sophisticated in numerous ways. These intricacies include the considerable variation within the morphology of box jellyfishes' eyes (including their task/behavior specification), and the molecular makeup of their eyes including: photoreceptors, opsins, lenses, and synapses. The comparison of these attributes to more derived visual systems can allow for a further understanding of how the evolution of more derived visual systems may have occurred, and puts into perspective how box jellyfish can play the role as an evolutionary/developmental model for all visual systems.

 

Characteristics

Box jellyfish visual systems are both diverse and complex, comprising multiple photosystems. There is likely considerable variation in visual properties between species of box jellyfish given the significant inter-species morphological and physiological variation. Eyes tend to differ in size and shape, along with number of receptors (including opsins), and physiology across species of box jellyfish.

 

Box jellyfish have a series of intricate lensed eyes that are similar to those of more derived multicellular organisms such as vertebrates. Their 24 eyes fit into four different morphological categories. These categories consist of two large, morphologically different medial eyes (a lower and upper lensed eye) containing spherical lenses, a lateral pair of pigment slit eyes, and a lateral pair of pigment pit eyes. The eyes are situated on rhopalia (small sensory structures) which serve sensory functions of the box jellyfish and arise from the cavities of the exumbrella (the surface of the body) on the side of the bells of the jellyfish. The two large eyes are located on the mid-line of the club and are considered complex because they contain lenses. The four remaining eyes lie laterally on either side of each rhopalia and are considered simple. The simple eyes are observed as small invaginated cups of epithelium that have developed pigmentation. The larger of the complex eyes contains a cellular cornea created by a mono ciliated epithelium, cellular lens, homogenous capsule to the lens, vitreous body with prismatic elements, and a retina of pigmented cells. The smaller of the complex eyes is said to be slightly less complex given that it lacks a capsule but otherwise contains the same structure as the larger eye.

 

Box jellyfish have multiple photosystems that comprise different sets of eyes. Evidence includes immunocytochemical and molecular data that show photopigment differences among the different morphological eye types, and physiological experiments done on box jellyfish to suggest behavioral differences among photosystems. Each individual eye type constitutes photosystems that work collectively to control visually guided behaviors.

 

Box jellyfish eyes primarily use c-PRCs (ciliary photoreceptor cells) similar to that of vertebrate eyes. These cells undergo phototransduction cascades (process of light absorption by photoreceptors) that are triggered by c-opsins. Available opsin sequences suggest that there are two types of opsins possessed by all cnidarians including an ancient phylogenetic opsin, and a sister ciliary opsin to the c-opsins group. Box jellyfish could have both ciliary and cnidops (cnidarian opsins), which is something not previously believed to appear in the same retina. Nevertheless, it is not entirely evident whether cnidarians possess multiple opsins that are capable of having distinctive spectral sensitivities.

 

Comparison with other organisms

Comparative research on genetic and molecular makeup of box jellyfishes' eyes versus more derived eyes seen in vertebrates and cephalopods focuses on: lenses and crystallin composition, synapses, and Pax genes and their implied evidence for shared primordial (ancestral) genes in eye evolution.

 

Box jellyfish eyes are said to be an evolutionary/developmental model of all eyes based on their evolutionary recruitment of crystallins and Pax genes. Research done on box jellyfish including Tripedalia cystophora has suggested that they possess a single Pax gene, PaxB. PaxB functions by binding to crystallin promoters and activating them. PaxB in situ hybridization resulted in PaxB expression in the lens, retina, and statocysts. These results and the rejection of the prior hypothesis that Pax6 was an ancestral Pax gene in eyes has led to the conclusion that PaxB was a primordial gene in eye evolution, and that the eyes of all organisms likely share a common ancestor.

 

The lens structure of box jellyfish appears very similar to those of other organisms, but the crystallins are distinct in both function and appearance. Weak reactions were seen within the sera and there were very weak sequence similarities within the crystallins among vertebrate and invertebrate lenses. This is likely due to differences in lower molecular weight proteins and the subsequent lack of immunological reactions with antisera that other organisms' lenses exhibit.

 

All four of the visual systems of box jellyfish species investigated with detail (Carybdea marsupialis, Chiropsalmus quadrumanus, Tamoya haplonema and Tripedalia cystophora) have invaginated synapses, but only in the upper and lower lensed eyes. Different densities were found between the upper and lower lenses, and between species. Four types of chemical synapses have been discovered within the rhopalia which could help in understanding neural organization including: clear unidirectional, dense-core unidirectional, clear bidirectional, and clear and dense-core bidirectional. The synapses of the lensed eyes could be useful as markers to learn more about the neural circuit in box jellyfish retinal areas.

 

Evolution as a response to natural stimuli

The primary adaptive responses to environmental variation observed in box jellyfish eyes include pupillary constriction speeds in response to light environments, as well as photoreceptor tuning and lens adaptations to better respond to shifts between light environments and darkness. Interestingly, some box jellyfish species' eyes appear to have evolved more focused vision in response to their habitat.

 

Pupillary contraction appears to have evolved in response to variation in the light environment across ecological niches across three species of box jellyfish (Chironex fleckeri, Chiropsella bronzie, and Carukia barnesi). Behavioral studies suggest that faster pupil contraction rates allow for greater object avoidance, and in fact, species with more complex habitats exhibit faster rates. Ch. bronzie inhabit shallow beach fronts that have low visibility and very few obstacles, thus, faster pupil contraction in response to objects in their environment is not important. Ca. barnesi and Ch. fleckeri are found in more three-dimensionally complex environments like mangroves with an abundance of natural obstacles, where faster pupil contraction is more adaptive. Behavioral studies support the idea that faster pupillary contraction rates assist with obstacle avoidance as well as depth adjustments in response to differing light intensities.

 

Light/dark adaptation via pupillary light reflexes is an additional form of an evolutionary response to the light environment. This relates to the pupil's response to shifts between light intensity (generally from sunlight to darkness). In the process of light/dark adaptation, the upper and lower lens eyes of different box jellyfish species vary in specific function. The lower lens-eyes contain pigmented photoreceptors and long pigment cells with dark pigments that migrate on light/dark adaptation, while the upper-lens eyes play a concentrated role in light direction and phototaxis given that they face upward towards the water surface (towards the sun or moon). The upper lens of Ch. bronzie does not exhibit any considerable optical power while Tr. cystophora (a box jellyfish species that tends to live in mangroves) does. The ability to use light to visually guide behavior is not of as much importance to Ch. bronzie as it is to species in more obstacle-filled environments. Differences in visually guided behavior serve as evidence that species that share the same number and structure of eyes can exhibit differences in how they control behavior.

 

Largest and smallest

Jellyfish range from about one millimeter in bell height and diameter, to nearly 2 metres (6+1⁄2 ft) in bell height and diameter; the tentacles and mouth parts usually extend beyond this bell dimension.

 

The smallest jellyfish are the peculiar creeping jellyfish in the genera Staurocladia and Eleutheria, which have bell disks from 0.5 millimetres (1⁄32 in) to a few millimeters in diameter, with short tentacles that extend out beyond this, which these jellyfish use to move across the surface of seaweed or the bottoms of rocky pools; many of these tiny creeping jellyfish cannot be seen in the field without a hand lens or microscope. They can reproduce asexually by fission (splitting in half). Other very small jellyfish, which have bells about one millimeter, are the hydromedusae of many species that have just been released from their parent polyps; some of these live only a few minutes before shedding their gametes in the plankton and then dying, while others will grow in the plankton for weeks or months. The hydromedusae Cladonema radiatum and Cladonema californicum are also very small, living for months, yet never growing beyond a few mm in bell height and diameter.

 

The lion's mane jellyfish, Cyanea capillata, was long-cited as the largest jellyfish, and arguably the longest animal in the world, with fine, thread-like tentacles that may extend up to 36.5 m (119 ft 9 in) long (though most are nowhere near that large). They have a moderately painful, but rarely fatal, sting. The increasingly common giant Nomura's jellyfish, Nemopilema nomurai, found in some, but not all years in the waters of Japan, Korea and China in summer and autumn is another candidate for "largest jellyfish", in terms of diameter and weight, since the largest Nomura's jellyfish in late autumn can reach 2 m (6 ft 7 in) in bell (body) diameter and about 200 kg (440 lb) in weight, with average specimens frequently reaching 0.9 m (2 ft 11 in) in bell diameter and about 150 kg (330 lb) in weight. The large bell mass of the giant Nomura's jellyfish can dwarf a diver and is nearly always much greater than the Lion's Mane, whose bell diameter can reach 1 m (3 ft 3 in).

 

The rarely encountered deep-sea jellyfish Stygiomedusa gigantea is another candidate for "largest jellyfish", with its thick, massive bell up to 100 cm (3 ft 3 in) wide, and four thick, "strap-like" oral arms extending up to 6 m (19+1⁄2 ft) in length, very different from the typical fine, threadlike tentacles that rim the umbrella of more-typical-looking jellyfish, including the Lion's Mane.

 

Desmonema glaciale, which lives in the Antarctic region, can reach a very large size (several meters). Purple-striped jelly (Chrysaora colorata) can also be extremely long (up to 15 feet).

 

Life history and behavior

Life cycle

Jellyfish have a complex life cycle which includes both sexual and asexual phases, with the medusa being the sexual stage in most instances. Sperm fertilize eggs, which develop into larval planulae, become polyps, bud into ephyrae and then transform into adult medusae. In some species certain stages may be skipped.

 

Upon reaching adult size, jellyfish spawn regularly if there is a sufficient supply of food. In most species, spawning is controlled by light, with all individuals spawning at about the same time of day; in many instances this is at dawn or dusk. Jellyfish are usually either male or female (with occasional hermaphrodites). In most cases, adults release sperm and eggs into the surrounding water, where the unprotected eggs are fertilized and develop into larvae. In a few species, the sperm swim into the female's mouth, fertilizing the eggs within her body, where they remain during early development stages. In moon jellies, the eggs lodge in pits on the oral arms, which form a temporary brood chamber for the developing planula larvae.

 

The planula is a small larva covered with cilia. When sufficiently developed, it settles onto a firm surface and develops into a polyp. The polyp generally consists of a small stalk topped by a mouth that is ringed by upward-facing tentacles. The polyps resemble those of closely related anthozoans, such as sea anemones and corals. The jellyfish polyp may be sessile, living on the bottom, boat hulls or other substrates, or it may be free-floating or attached to tiny bits of free-living plankton or rarely, fish or other invertebrates. Polyps may be solitary or colonial. Most polyps are only millimetres in diameter and feed continuously. The polyp stage may last for years.

 

After an interval and stimulated by seasonal or hormonal changes, the polyp may begin reproducing asexually by budding and, in the Scyphozoa, is called a segmenting polyp, or a scyphistoma. Budding produces more scyphistomae and also ephyrae. Budding sites vary by species; from the tentacle bulbs, the manubrium (above the mouth), or the gonads of hydromedusae. In a process known as strobilation, the polyp's tentacles are reabsorbed and the body starts to narrow, forming transverse constrictions, in several places near the upper extremity of the polyp. These deepen as the constriction sites migrate down the body, and separate segments known as ephyra detach. These are free-swimming precursors of the adult medusa stage, which is the life stage that is typically identified as a jellyfish. The ephyrae, usually only a millimeter or two across initially, swim away from the polyp and grow. Limnomedusae polyps can asexually produce a creeping frustule larval form, which crawls away before developing into another polyp. A few species can produce new medusae by budding directly from the medusan stage. Some hydromedusae reproduce by fission.

 

Lifespan

Little is known of the life histories of many jellyfish as the places on the seabed where the benthic forms of those species live have not been found. However, an asexually reproducing strobila form can sometimes live for several years, producing new medusae (ephyra larvae) each year.

 

An unusual species, Turritopsis dohrnii, formerly classified as Turritopsis nutricula, might be effectively immortal because of its ability under certain circumstances to transform from medusa back to the polyp stage, thereby escaping the death that typically awaits medusae post-reproduction if they have not otherwise been eaten by some other organism. So far this reversal has been observed only in the laboratory.

 

Locomotion

Jellyfish locomotion is highly efficient. Muscles in the jellylike bell contract, setting up a start vortex and propelling the animal. When the contraction ends, the bell recoils elastically, creating a stop vortex with no extra energy input.

Using the moon jelly Aurelia aurita as an example, jellyfish have been shown to be the most energy-efficient swimmers of all animals. They move through the water by radially expanding and contracting their bell-shaped bodies to push water behind them. They pause between the contraction and expansion phases to create two vortex rings. Muscles are used for the contraction of the body, which creates the first vortex and pushes the animal forward, but the mesoglea is so elastic that the expansion is powered exclusively by relaxing the bell, which releases the energy stored from the contraction. Meanwhile, the second vortex ring starts to spin faster, sucking water into the bell and pushing against the centre of the body, giving a secondary and "free" boost forward. The mechanism, called passive energy recapture, only works in relatively small jellyfish moving at low speeds, allowing the animal to travel 30 percent farther on each swimming cycle. Jellyfish achieved a 48 percent lower cost of transport (food and oxygen intake versus energy spent in movement) than other animals in similar studies. One reason for this is that most of the gelatinous tissue of the bell is inactive, using no energy during swimming.

 

Ecology

Diet

Jellyfish are, like other cnidarians, generally carnivorous (or parasitic), feeding on planktonic organisms, crustaceans, small fish, fish eggs and larvae, and other jellyfish, ingesting food and voiding undigested waste through the mouth. They hunt passively using their tentacles as drift lines, or sink through the water with their tentacles spread widely; the tentacles, which contain nematocysts to stun or kill the prey, may then flex to help bring it to the mouth. Their swimming technique also helps them to capture prey; when their bell expands it sucks in water which brings more potential prey within reach of the tentacles.

 

A few species such as Aglaura hemistoma are omnivorous, feeding on microplankton which is a mixture of zooplankton and phytoplankton (microscopic plants) such as dinoflagellates. Others harbour mutualistic algae (Zooxanthellae) in their tissues; the spotted jellyfish (Mastigias papua) is typical of these, deriving part of its nutrition from the products of photosynthesis, and part from captured zooplankton. The upside-down jellyfish (Cassiopea andromeda) also has a symbiotic relationship with microalgae, but captures tiny animals to supplement their diet. This is done by releasing tiny balls of living cells composed of mesoglea. These use cilia to drive them through water and stinging cells which stun the prey. The blobs also seems to have digestive capabilities.

 

Predation

Other species of jellyfish are among the most common and important jellyfish predators. Sea anemones may eat jellyfish that drift into their range. Other predators include tunas, sharks, swordfish, sea turtles and penguins. Jellyfish washed up on the beach are consumed by foxes, other terrestrial mammals and birds. In general however, few animals prey on jellyfish; they can broadly be considered to be top predators in the food chain. Once jellyfish have become dominant in an ecosystem, for example through overfishing which removes predators of jellyfish larvae, there may be no obvious way for the previous balance to be restored: they eat fish eggs and juvenile fish, and compete with fish for food, preventing fish stocks from recovering.

 

Symbiosis

Some small fish are immune to the stings of the jellyfish and live among the tentacles, serving as bait in a fish trap; they are safe from potential predators and are able to share the fish caught by the jellyfish. The cannonball jellyfish has a symbiotic relationship with ten different species of fish, and with the longnose spider crab, which lives inside the bell, sharing the jellyfish's food and nibbling its tissues.

 

Main article: Jellyfish bloom

Jellyfish form large masses or blooms in certain environmental conditions of ocean currents, nutrients, sunshine, temperature, season, prey availability, reduced predation and oxygen concentration. Currents collect jellyfish together, especially in years with unusually high populations. Jellyfish can detect marine currents and swim against the current to congregate in blooms. Jellyfish are better able to survive in nutrient-rich, oxygen-poor water than competitors, and thus can feast on plankton without competition. Jellyfish may also benefit from saltier waters, as saltier waters contain more iodine, which is necessary for polyps to turn into jellyfish. Rising sea temperatures caused by climate change may also contribute to jellyfish blooms, because many species of jellyfish are able to survive in warmer waters. Increased nutrients from agricultural or urban runoff with nutrients including nitrogen and phosphorus compounds increase the growth of phytoplankton, causing eutrophication and algal blooms. When the phytoplankton die, they may create dead zones, so-called because they are hypoxic (low in oxygen). This in turn kills fish and other animals, but not jellyfish, allowing them to bloom. Jellyfish populations may be expanding globally as a result of land runoff and overfishing of their natural predators. Jellyfish are well placed to benefit from disturbance of marine ecosystems. They reproduce rapidly; they prey upon many species, while few species prey on them; and they feed via touch rather than visually, so they can feed effectively at night and in turbid waters. It may be difficult for fish stocks to re-establish themselves in marine ecosystems once they have become dominated by jellyfish, because jellyfish feed on plankton, which includes fish eggs and larvae.

 

As suspected at the turn of this century, jellyfish blooms are increasing in frequency. Between 2013 and 2020 the Mediterranean Science Commission monitored on a weekly basis the frequency of such outbreaks in coastal waters from Morocco to the Black Sea, revealing a relatively high frequency of these blooms nearly all year round, with peaks observed from March to July and often again in the autumn. The blooms are caused by different jellyfish species, depending on their localisation within the Basin: one observes a clear dominance of Pelagia noctiluca and Velella velella outbreaks in the western Mediterranean, of Rhizostoma pulmo and Rhopilema nomadica outbreaks in the eastern Mediterranean, and of Aurelia aurita and Mnemiopsis leidyi outbreaks in the Black Sea.

 

Some jellyfish populations that have shown clear increases in the past few decades are invasive species, newly arrived from other habitats: examples include the Black Sea, Caspian Sea, Baltic Sea, central and eastern Mediterranean, Hawaii, and tropical and subtropical parts of the West Atlantic (including the Caribbean, Gulf of Mexico and Brazil).

 

Jellyfish blooms can have significant impact on community structure. Some carnivorous jellyfish species prey on zooplankton while others graze on primary producers. Reductions in zooplankton and ichthyoplankton due to a jellyfish bloom can ripple through the trophic levels. High-density jellyfish populations can outcompete other predators and reduce fish recruitment. Increased grazing on primary producers by jellyfish can also interrupt energy transfer to higher trophic levels.

 

During blooms, jellyfish significantly alter the nutrient availability in their environment. Blooms require large amounts of available organic nutrients in the water column to grow, limiting availability for other organisms. Some jellyfish have a symbiotic relationship with single-celled dinoflagellates, allowing them to assimilate inorganic carbon, phosphorus, and nitrogen creating competition for phytoplankton. Their large biomass makes them an important source of dissolved and particulate organic matter for microbial communities through excretion, mucus production, and decomposition. The microbes break down the organic matter into inorganic ammonium and phosphate. However, the low carbon availability shifts the process from production to respiration creating low oxygen areas making the dissolved inorganic nitrogen and phosphorus largely unavailable for primary production.

 

These blooms have very real impacts on industries. Jellyfish can outcompete fish by utilizing open niches in over-fished fisheries. Catch of jellyfish can strain fishing gear and lead to expenses relating to damaged gear. Power plants have been shut down due to jellyfish blocking the flow of cooling water. Blooms have also been harmful for tourism, causing a rise in stings and sometimes the closure of beaches.

 

Jellyfish form a component of jelly-falls, events where gelatinous zooplankton fall to the seafloor, providing food for the benthic organisms there. In temperate and subpolar regions, jelly-falls usually follow immediately after a bloom.

 

Habitats

Most jellyfish are marine animals, although a few hydromedusae inhabit freshwater. The best known freshwater example is the cosmopolitan hydrozoan jellyfish, Craspedacusta sowerbii. It is less than an inch (2.5 cm) in diameter, colorless and does not sting. Some jellyfish populations have become restricted to coastal saltwater lakes, such as Jellyfish Lake in Palau. Jellyfish Lake is a marine lake where millions of golden jellyfish (Mastigias spp.) migrate horizontally across the lake daily.

 

Although most jellyfish live well off the ocean floor and form part of the plankton, a few species are closely associated with the bottom for much of their lives and can be considered benthic. The upside-down jellyfish in the genus Cassiopea typically lie on the bottom of shallow lagoons where they sometimes pulsate gently with their umbrella top facing down. Even some deep-sea species of hydromedusae and scyphomedusae are usually collected on or near the bottom. All of the stauromedusae are found attached to either seaweed or rocky or other firm material on the bottom.

 

Some species explicitly adapt to tidal flux. In Roscoe Bay, jellyfish ride the current at ebb tide until they hit a gravel bar, and then descend below the current. They remain in still waters until the tide rises, ascending and allowing it to sweep them back into the bay. They also actively avoid fresh water from mountain snowmelt, diving until they find enough salt.

  

Parasites

Jellyfish are hosts to a wide variety of parasitic organisms. They act as intermediate hosts of endoparasitic helminths, with the infection being transferred to the definitive host fish after predation. Some digenean trematodes, especially species in the family Lepocreadiidae, use jellyfish as their second intermediate hosts. Fish become infected by the trematodes when they feed on infected jellyfish.

 

Relation to humans

Jellyfish have long been eaten in some parts of the world. Fisheries have begun harvesting the American cannonball jellyfish, Stomolophus meleagris, along the southern Atlantic coast of the United States and in the Gulf of Mexico for export to Asia.

 

Jellyfish are also harvested for their collagen, which is being investigated for use in a variety of applications including the treatment of rheumatoid arthritis.

 

Aquaculture and fisheries of other species often suffer severe losses – and so losses of productivity – due to jellyfish.

 

Products

Main article: Jellyfish as food

In some countries, including China, Japan, and Korea, jellyfish are a delicacy. The jellyfish is dried to prevent spoiling. Only some 12 species of scyphozoan jellyfish belonging to the order Rhizostomeae are harvested for food, mostly in southeast Asia. Rhizostomes, especially Rhopilema esculentum in China (海蜇 hǎizhé, 'sea stingers') and Stomolophus meleagris (cannonball jellyfish) in the United States, are favored because of their larger and more rigid bodies and because their toxins are harmless to humans.

 

Traditional processing methods, carried out by a jellyfish master, involve a 20- to 40-day multi-phase procedure in which, after removing the gonads and mucous membranes, the umbrella and oral arms are treated with a mixture of table salt and alum, and compressed. Processing makes the jellyfish drier and more acidic, producing a crisp texture. Jellyfish prepared this way retain 7–10% of their original weight, and the processed product consists of approximately 94% water and 6% protein. Freshly processed jellyfish has a white, creamy color and turns yellow or brown during prolonged storage.

 

In China, processed jellyfish are desalted by soaking in water overnight and eaten cooked or raw. The dish is often served shredded with a dressing of oil, soy sauce, vinegar and sugar, or as a salad with vegetables. In Japan, cured jellyfish are rinsed, cut into strips and served with vinegar as an appetizer. Desalted, ready-to-eat products are also available.

 

Biotechnology

The hydromedusa Aequorea victoria was the source of green fluorescent protein, studied for its role in bioluminescence and later for use as a marker in genetic engineering.

Pliny the Elder reported in his Natural History that the slime of the jellyfish "Pulmo marinus" produced light when rubbed on a walking stick.

 

In 1961, Osamu Shimomura extracted green fluorescent protein (GFP) and another bioluminescent protein, called aequorin, from the large and abundant hydromedusa Aequorea victoria, while studying photoproteins that cause bioluminescence in this species. Three decades later, Douglas Prasher sequenced and cloned the gene for GFP. Martin Chalfie figured out how to use GFP as a fluorescent marker of genes inserted into other cells or organisms. Roger Tsien later chemically manipulated GFP to produce other fluorescent colors to use as markers. In 2008, Shimomura, Chalfie and Tsien won the Nobel Prize in Chemistry for their work with GFP. Man-made GFP became widely used as a fluorescent tag to show which cells or tissues express specific genes. The genetic engineering technique fuses the gene of interest to the GFP gene. The fused DNA is then put into a cell, to generate either a cell line or (via IVF techniques) an entire animal bearing the gene. In the cell or animal, the artificial gene turns on in the same tissues and the same time as the normal gene, making a fusion of the normal protein with GFP attached to the end, illuminating the animal or cell reveals what tissues express that protein—or at what stage of development. The fluorescence shows where the gene is expressed.

 

Aquarium display

Jellyfish are displayed in many public aquariums. Often the tank's background is blue and the animals are illuminated by side light, increasing the contrast between the animal and the background. In natural conditions, many jellies are so transparent that they are nearly invisible. Jellyfish are not adapted to closed spaces. They depend on currents to transport them from place to place. Professional exhibits as in the Monterey Bay Aquarium feature precise water flows, typically in circular tanks to avoid trapping specimens in corners. The outflow is spread out over a large surface area and the inflow enters as a sheet of water in front of the outflow, so the jellyfish do not get sucked into it. As of 2009, jellyfish were becoming popular in home aquariums, where they require similar equipment.

 

Stings

Jellyfish are armed with nematocysts, a type of specialized stinging cell. Contact with a jellyfish tentacle can trigger millions of nematocysts to pierce the skin and inject venom, but only some species' venom causes an adverse reaction in humans. In a study published in Communications Biology, researchers found a jellyfish species called Cassiopea xamachana which when triggered will release tiny balls of cells that swim around the jellyfish stinging everything in their path. Researchers described these as "self-propelling microscopic grenades" and named them cassiosomes.

 

The effects of stings range from mild discomfort to extreme pain and death. Most jellyfish stings are not deadly, but stings of some box jellyfish (Irukandji jellyfish), such as the sea wasp, can be deadly. Stings may cause anaphylaxis (a form of shock), which can be fatal. Jellyfish kill 20 to 40 people a year in the Philippines alone. In 2006 the Spanish Red Cross treated 19,000 stung swimmers along the Costa Brava.

 

Vinegar (3–10% aqueous acetic acid) may help with box jellyfish stings but not the stings of the Portuguese man o' war. Clearing the area of jelly and tentacles reduces nematocyst firing. Scraping the affected skin, such as with the edge of a credit card, may remove remaining nematocysts. Once the skin has been cleaned of nematocysts, hydrocortisone cream applied locally reduces pain and inflammation. Antihistamines may help to control itching. Immunobased antivenins are used for serious box jellyfish stings.

 

In Elba Island and Corsica dittrichia viscosa is now used by residents and tourists to heal stings from jellyfish, bees and wasps pressing fresh leaves on the skin with quick results.

 

Mechanical issues

Jellyfish in large quantities can fill and split fishing nets and crush captured fish. They can clog cooling equipment, having disabled power stations in several countries; jellyfish caused a cascading blackout in the Philippines in 1999, as well as damaging the Diablo Canyon Power Plant in California in 2008. They can also stop desalination plants and ships' engines.

CHANGI NAVAL BASE, Singapore (Jan. 3, 2017) Sailors conduct boat operations using a twin boom extensible crane to lower a rigid hull inflatable boat (RHIB) into the water aboard littoral combat ship USS Coronado (LCS 4). Currently on a rotational deployment in support of the Asia-Pacific Rebalance, Coronado is a fast and agile warship tailor-made to patrol the region's littorals and work hull-to-hull with partner navies, providing 7th Fleet with the flexible capabilities it needs now and in the future. (U.S. Navy photo by Mass Communication Specialist 2nd Class Amy M. Ressler/Released)

Mespilia globulus (Temnopleuridae)

 

Distribution: Coastal waters of Asia from India to Southern Japan.

 

Habitat: Coral reefs. During daylight hides among rocks, in crevices, or under plants in a sandy substrate.

 

Appearance: Diameter to 8 cm. Red to brown short, sharp spines are separated by ten bluevelvet regions where spines are absent.

 

Diet: Primarily a nocturnal feeder on coralline algae, also green filamentous algae. Grazes by

scraping with its Aristotle’s lantern apparatus, as do all sea urchins.

 

Remarks: Camouflages itself with various items such as rubble and detritus Pedicellariae are constructed of several small spines which have become modified to articulate with one another and function as snapping jaws. Each pedicalliria is typically found on an elongate and extensible stalk, and they reach out to pinch any small animals or body parts, such as the adhesive tube feet of a predatory sea star, that threaten the sea urchin.

 

Color Cluster

 

4-21-16

ANDAMAN SEA (Dec. 13, 2021) Mineman 2nd Class Arthur Guevara, from Orizaba, Mexico, operates the twin boom extensible crane (TBEC) during boat operations aboard the Independence-variant littoral combat ship USS Tulsa (LCS 16). Tulsa, part of Destroyer Squadron (DESRON) 7, is on a rotational deployment, operating in U.S. 7th Fleet to enhance interoperability with partners and serve as a ready-response force in support of a free and open Indo-Pacific region. (U.S. Navy photo by Mass Communication Specialist 1st Class Devin M. Langer)

A blockchain, originally block chain, is a continuously growing list of records, called blocks, which are linked and secured using cryptography. Each block typically contains a cryptographic hash of the previous block, a timestamp and transaction data. By design, a blockchain is inherently resistant to modification of the data. It is "an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way". For use as a distributed ledger, a blockchain is typically managed by a peer-to-peer network collectively adhering to a protocol for validating new blocks. Once recorded, the data in any given block cannot be altered retroactively without the alteration of all subsequent blocks, which requires collusion of the network majority. Blockchains are secure by design and are an example of a distributed computing system with high Byzantine fault tolerance. Decentralized consensus has therefore been achieved with a blockchain. This makes blockchains potentially suitable for the recording of events, medical records, and other records management activities, such as identity management,transaction processing, documenting provenance, food traceability or voting. Blockchain was invented by Satoshi Nakamoto in 2008 for use in the cryptocurrency bitcoin, as its public transaction ledger.The first work on a cryptographically secured chain of blocks was described in 1991 by Stuart Haber and W. Scott Stornetta.In 1992, Bayer, Haber and Stornetta incorporated Merkle trees to the design, which improved its efficiency by allowing several documents to be collected into one block.In 2002, David Mazières and Dennis Shasha proposed a network file system with decentralized trust: writers to the file system trust one another but not the network in between; they achieve file system integrity by writing signed commits to a shared, append-only signature chain that captures the root of the file system (which in turn is a Merkle Tree). This system can be viewed as a proto-blockchain in which all authorized clients can always write, whereas, in modern blockchains, a client who solves a cryptographic puzzle can write one block.[citation needed] In 2005, Nick Szabo proposed a blockchain-like system for decentralized property titles and his bit gold payment system that utilised chained proof-of-work and timestamping. However, Szabo's method of double-spending protection was vulnerable to Sybil attacks. The first blockchain was conceptualised by a person (or group of people) known as Satoshi Nakamoto in 2008. It was implemented the following year by Nakamoto as a core component of the cryptocurrency bitcoin, where it serves as the public ledger for all transactions on the network.Through the use of a blockchain, bitcoin became the first digital currency to solve the double spending problem without requiring a trusted authority and has been the inspiration for many additional applications. In August 2014, the bitcoin blockchain file size, containing records of all transactions that have occurred on the network, reached 20GB (gigabytes). In January 2015, the size had grown to almost 30GB, and from January 2016 to January 2017, the bitcoin blockchain grew from 50GB to 100GB in size.The words block and chain were used separately in Satoshi Nakamoto's original paper, but were eventually popularized as a single word, blockchain, by 2016. The term blockchain 2.0 refers to new applications of the distributed blockchain database, first emerging in 2014. The Economist described one implementation of this second-generation programmable blockchain as coming with "a programming language that allows users to write more sophisticated smart contracts, thus creating invoices that pay themselves when a shipment arrives or share certificates which automatically send their owners dividends if profits reach a certain level". Blockchain 2.0 technologies go beyond transactions and enable "exchange of value without powerful intermediaries acting as arbiters of money and information". They are expected to enable excluded people to enter the global economy, protect the privacy of participants, allow people to "monetize their own information", and provide the capability to ensure creators are compensated for their intellectual property. Second-generation blockchain technology makes it possible to store an individual's "persistent digital ID and persona" and are providing an avenue to help solve the problem of social inequality by "potentially changing the way wealth is distributed".:14–15 As of 2016, blockchain 2.0 implementations continue to require an off-chain oracle to access any "external data or events based on time or market conditions [that need] to interact with the blockchain". In 2016, the central securities depository of the Russian Federation (NSD) announced a pilot project, based on the Nxt blockchain 2.0 platform, that would explore the use of blockchain-based automated voting systems. IBM opened a blockchain innovation research center in Singapore in July 2016. A working group for the World Economic Forum met in November 2016 to discuss the development of governance models related to blockchain.[28] According to Accenture, an application of the diffusion of innovations theory suggests that blockchains attained a 13.5% adoption rate within financial services in 2016, therefore reaching the early adopters phase. Industry trade groups joined to create the Global Blockchain Forum in 2016, an initiative of the Chamber of Digital Commerce. A blockchain is a decentralized, distributed and public digital ledger that is used to record transactions across many computers so that the record cannot be altered retroactively without the alteration of all subsequent blocks and the collusion of the network. This allows the participants to verify and audit transactions inexpensively. A blockchain database is managed autonomously using a peer-to-peer network and a distributed timestamping server. They are authenticated by mass collaboration powered by collective self-interests.The result is a robust workflow where participants' uncertainty regarding data security is marginal. The use of a blockchain removes the characteristic of infinite reproducibility from a digital asset. It confirms that each unit of value was transferred only once, solving the long-standing problem of double spending. Blockchains have been described as a value-exchange protocol. This blockchain-based exchange of value can be completed more quickly, more safely and more cheaply than with traditional systems. A blockchain can assign title rights because it provides a record that compels offer and acceptance.

 

Blocks

Blocks hold batches of valid transactions that are hashed and encoded into a Merkle tree. Each block includes the cryptographic hash of the prior block in the blockchain, linking the two. The linked blocks form a chain.This iterative process confirms the integrity of the previous block, all the way back to the original genesis block.

 

Sometimes separate blocks can be produced concurrently, creating a temporary fork. In addition to a secure hash-based history, any blockchain has a specified algorithm for scoring different versions of the history so that one with a higher value can be selected over others. Blocks not selected for inclusion in the chain are called orphan blocks. Peers supporting the database have different versions of the history from time to time. They only keep the highest-scoring version of the database known to them. Whenever a peer receives a higher-scoring version (usually the old version with a single new block added) they extend or overwrite their own database and retransmit the improvement to their peers. There is never an absolute guarantee that any particular entry will remain in the best version of the history forever. Because blockchains are typically built to add the score of new blocks onto old blocks and because there are incentives to work only on extending with new blocks rather than overwriting old blocks, the probability of an entry becoming superseded goes down exponentially as more blocks are built on top of it, eventually becoming very low. For example, in a blockchain using the proof-of-work system, the chain with the most cumulative proof-of-work is always considered the valid one by the network. There are a number of methods that can be used to demonstrate a sufficient level of computation. Within a blockchain the computation is carried out redundantly rather than in the traditional segregated and parallel manner.

 

The block time is the average time it takes for the network to generate one extra block in the blockchain. Some blockchains create a new block as frequently as every five seconds. By the time of block completion, the included data becomes verifiable. In cryptocurrency, this is practically when the money transaction takes place, so a shorter block time means faster transactions. The block time for Ethereum is set to between 14 and 15 seconds, while for bitcoin it is 10 minutes.Express. Why is Ripple XRP falling today? Why is it crashing in value?Ripple price: Why is Ripple XRP falling today? Why is it… 'Ripple is first in line' - CEO reveals next cryptocurrency to catch up with bitcoin

'Ripple is first in line' - CEO reveals next cryptocurrency to…

Ripple price news: Why is XRP falling so fast? What's happening to Ripple?Ripple price news: Why is XRP falling so fast? What's happening… Bitcoin price BOOST: Big investors are FINALLY realising Bitcoin is GAME-CHANGING Bitcoin price WARNING: CEO says cryptocurrency has 'NOTHING to do with the real economy' BITCOIN has come under fire from the CEO of Euronext as the financial expert claimed the cryptocurrency "has nothing to do with the real economy".

Bitcoin price suffered a massive plunge as the cryptocurrency reached the value of $9,114.56, according to Coindesk at 10:37 pm on February. As the crypto-craze started to die down, Euronext CEO Stéphane Boujnah claims bitcoin cannot even be classified as a cryptocurrency. Speaking on Bloomberg, Mr Boujnah said Euronext will never open a bitcoin market. He said: "We will not create a bitcoin market because the mandate of Euronext is to power Pan-European capital markets to finance the real economy and bitcoin has nothing to do with the real economy. "Bitcoin has a lot to do with bitcoin. And we believe bitcoin is not a cryptocurrency.

"Bitcoin is at best a crypto asset. All currencies are assets but not all assets are currencies. "Clearly, bitcoin today is just like a piece of art, or just like a diamond, just like a Pokemon card.

"It can be anything to capture value but today people buy it because it goes up and because it’s not as serious and transparent as a lot of assets. "So great, good luck. Like any emerging assets, it’s very fancy, which is great, but this is not our mandate. "Our mandate is to be the place regulated, transparent, open, reliable. It’s not our mandate to be part of this new game in town." Despite the rollercoaster few months suffered by the crypto mania, bitcoin and other cryptocurrencies such as Ripple and ethereum still benefit from a "growing" appreciation among institutional investors, according to Dr Garrick Hileman, from the Cambridge University Centre for Alternative Finance.In an exclusive interview with Express.co.uk, Dr Hileman said: "Any breakthrough technology, and bitcoin and blockchain, are certainly breakthrough technologies, hype often outpaces the reality. “In terms of both of how mature the technology is, the rates of adoption. “We’ve seen this before with bitcoin and we’ve seen the price shoot up first in late 2013 when it first entered the mainstream public consciousness. “The price subsequently crashed 85 percent as security at a major exchange broke down and bitcoin’s were stolen. “So we’ve seen this kind of story repeat where bitcoin rises, gets hyped and then there’s a crash.” This section is transcluded from Fork (blockchain). A hard fork occurs when a blockchain splits into two incompatible separate chains. This is a consequence of the use of two incompatible sets of rules trying to govern the system. For example, Ethereum has hard-forked to "make whole" the investors in The DAO, which had been hacked by exploiting a vulnerability in its code. In 2014 the Nxt community was asked to consider a hard fork that would have led to a rollback of the blockchain records to mitigate the effects of a theft of 50 million NXT from a major cryptocurrency exchange. The hard fork proposal was rejected, and some of the funds were recovered after negotiations and ransom payment.

Decentralization

By storing data across its network, the blockchain eliminates the risks that come with data being held centrally. The decentralized blockchain may use ad-hoc message passing and distributed networking. Its network lacks centralized points of vulnerability that computer crackers can exploit; likewise, it has no central point of failure. Blockchain security methods include the use of public-key cryptography. A public key (a long, random-looking string of numbers) is an address on the blockchain. Value tokens sent across the network are recorded as belonging to that address. A private key is like a password that gives its owner access to their digital assets or the means to otherwise interact with the various capabilities that blockchains now support. Data stored on the blockchain is generally considered incorruptible. This is where blockchain has its advantage. While centralized data is more controllable, information and data manipulation are common. By decentralizing it, blockchain makes data transparent to everyone involved. Every node in a decentralized system has a copy of the blockchain. Data quality is maintained by massive database replication[9] and computational trust. No centralized "official" copy exists and no user is "trusted" more than any other. Transactions are broadcast to the network using software. Messages are delivered on a best-effort basis. Mining nodes validate transactions, add them to the block they are building, and then broadcast the completed block to other nodes. Blockchains use various time-stamping schemes, such as proof-of-work, to serialize changes. Alternate consensus methods include proof-of-stake. Growth of a decentralized blockchain is accompanied by the risk of node centralization because the computer resources required to process larger amounts of data become more expensive.

 

Openness

Open blockchains are more user-friendly than some traditional ownership records, which, while open to the public, still require physical access to view. Because all early blockchains were permissionless, controversy has arisen over the blockchain definition. An issue in this ongoing debate is whether a private system with verifiers tasked and authorized (permissioned) by a central authority should be considered a blockchain. Proponents of permissioned or private chains argue that the term "blockchain" may be applied to any data structure that batches data into time-stamped blocks. These blockchains serve as a distributed version of multiversion concurrency control (MVCC) in databases. Just as MVCC prevents two transactions from concurrently modifying a single object in a database, blockchains prevent two transactions from spending the same single output in a blockchain.[24]:30–31 Opponents say that permissioned systems resemble traditional corporate databases, not supporting decentralized data verification, and that such systems are not hardened against operator tampering and revision. Nikolai Hampton of Computerworld said that "many in-house blockchain solutions will be nothing more than cumbersome databases."Business analysts Don Tapscott and Alex Tapscott define blockchain as a distributed ledger or database open to anyone.

 

Permissionless

The great advantage to an open, permissionless, or public, blockchain network is that guarding against bad actors is not required and no access control is needed.This means that applications can be added to the network without the approval or trust of others, using the blockchain as a transport layer.

 

Bitcoin and other cryptocurrencies currently secure their blockchain by requiring new entries including a proof of work. To prolong the blockchain, bitcoin uses Hashcash puzzles developed by Adam Back in the 1990s.

 

Financial companies have not prioritised decentralized blockchains. In 2016, venture capital investment for blockchain related projects was weakening in the USA but increasing in China. Bitcoin and many other cryptocurrencies use open (public) blockchains. As of January 2018, bitcoin has the highest market capitalization.

 

Permissioned (private) blockchain

 

Permissioned blockchains use an access control layer to govern who has access to the network. In contrast to public blockchain networks, validators on private blockchain networks are vetted by the network owner. They do not rely on anonymous nodes to validate transactions nor do they benefit from the network effect. Permissioned blockchains can also go by the name of 'consortium' or 'hybrid' blockchains.

 

The New York Times noted in both 2016 and 2017 that many corporations are using blockchain networks "with private blockchains, independent of the public system."

 

Disadvantages

Nikolai Hampton pointed out in Computerworld that "There is also no need for a "51 percent" attack on a private blockchain, as the private blockchain (most likely) already controls 100 percent of all block creation resources. If you could attack or damage the blockchain creation tools on a private corporate server, you could effectively control 100 percent of their network and alter transactions however you wished." This has a set of particularly profound adverse implications during a financial crisis or debt crisis like the financial crisis of 2007–08, where politically powerful actors may make decisions that favor some groups at the expense of others.[citation needed] and "the bitcoin blockchain is protected by the massive group mining effort. It's unlikely that any private blockchain will try to protect records using gigawatts of computing power — it's time consuming and expensive."He also said, "Within a private blockchain there is also no 'race'; there's no incentive to use more power or discover blocks faster than competitors. This means that many in-house blockchain solutions will be nothing more than cumbersome databases."

 

Uses

Blockchain technology can be integrated into multiple areas. The primary use of blockchains today is as a distributed ledger for cryptocurrencies, most notably bitcoin.While a few central banks, in countries such as China, United States, Sweden, Singapore, South Africa and England are studying issuance of a Central Bank Issued Cryptocurrency (CICC), none have done so thus far.

 

General potentials

Blockchain technology has a large potential to transform business operating models in the long term. Blockchain distributed ledger technology is more a foundational technology—with the potential to create new foundations for global economic and social systems—than a disruptive technology, which typically "attack a traditional business model with a lower-cost solution and overtake incumbent firms quickly".Even so, there are a few operational products maturing from proof of concept by late 2016.The use of blockchains promises to bring significant efficiencies to global supply chains, financial transactions, asset ledgers and decentralized social networking.

 

As of 2016, some observers remain skeptical. Steve Wilson, of Constellation Research, believes the technology has been hyped with unrealistic claims.To mitigate risk businesses are reluctant to place blockchain at the core of the business structure.

 

This means specific blockchain applications may be a disruptive innovation, because substantially lower-cost solutions can be instantiated, which can disrupt existing business models. Blockchain protocols facilitate businesses to use new methods of processing digital transactions.[68] Examples include a payment system and digital currency, facilitating crowdsales, or implementing prediction markets and generic governance tools.

 

Blockchains alleviate the need for a trust service provider and are predicted to result in less capital being tied up in disputes. Blockchains have the potential to reduce systemic risk and financial fraud. They automate processes that were previously time-consuming and done manually, such as the incorporation of businesses.In theory, it would be possible to collect taxes, conduct conveyancing and provide risk management with blockchains.

 

As a distributed ledger, blockchain reduces the costs involved in verifying transactions, and by removing the need for trusted "third-parties" such as banks to complete transactions, the technology also lowers the cost of networking, therefore allowing several applications.

 

Starting with a strong focus on financial applications, blockchain technology is extending to activities including decentralized applications and collaborative organizations that eliminate a middleman.

 

Land registration

"Land is a financial source, if people can prove they own it, they can borrow against it."

Emmanuel Noah, CEO of Ghanian startup BenBen, New York Observer

Frameworks and trials such as the one at the Sweden Land Registry aim to demonstrate the effectiveness of the blockchain at speeding land sale deals.The Republic of Georgia is piloting a blockchain-based property registry.The Ethical and Fair Creators Association uses blockchain to help startups protect their authentic ideas.

 

The Government of India is fighting land fraud with the help of a blockchain.

 

In October 2017, one of the first international property transactions was completed successfully using a blockchain-based smart contract.

 

In the first half of 2018, an experiment will be conducted on the use of blocking technology to monitor the reliability of the Unified State Real Estate Register (USRER) data in the territory of Moscow.

 

The Big Four

Each of the Big Four accounting firms is testing blockchain technologies in various formats. Ernst & Young has provided cryptocurrency wallets to all (Swiss) employees,has installed a bitcoin ATM in their office in Switzerland, and accepts bitcoin as payment for all its consulting services. Marcel Stalder, CEO of Ernst & Young Switzerland, stated, "We don't only want to talk about digitalization, but also actively drive this process together with our employees and our clients. It is important to us that everybody gets on board and prepares themselves for the revolution set to take place in the business world through blockchains, [to] smart contracts and digital currencies."PwC, Deloitte, and KPMG have taken a different path from Ernst & Young and are all testing private blockchains.

 

Smart contracts

Blockchain-based smart contracts are contracts that can be partially or fully executed or enforced without human interaction.One of the main objectives of a smart contract is automated escrow. The IMF believes blockchains could reduce moral hazards and optimize the use of contracts in general.Due to the lack of widespread use their legal status is unclear.

 

Some blockchain implementations could enable the coding of contracts that will execute when specified conditions are met. A blockchain smart contract would be enabled by extensible programming instructions that define and execute an agreement.For example, Ethereum Solidity is an open-source blockchain project that was built specifically to realize this possibility by implementing a Turing-complete programming language capability to implement such contracts.

 

Nonprofit organizations

Level One Project from the Bill & Melinda Gates Foundation aims to use blockchain technology to help the two billion people worldwide who lack bank accounts.

Building Blocks project from the U.N.'s World Food Programme (WFP) aims to make WFP's growing cash-based transfer operations faster, cheaper, and more secure. Building Blocks commenced field pilots in Pakistan in January 2017 that will continue throughout spring.

Decentralized networks

The Backfeed project develops a distributed governance system for blockchain-based applications allowing for the collaborative creation and distribution of value in spontaneously emerging networks of peers.[88][89]

The Alexandria project is a blockchain-based Decentralized Library.

Tezos is a blockchain project that governs itself by voting of its token holders. Bitcoin blockchain performs as a cryptocurrency and payment system. Ethereum blockchain added smart contract system on top of a blockchain. Tezos blockchain will add an autonomy system – a decentralized code Development function on top of both bitcoin and Ethereum blockchains.

Governments and national currencies

The director of the Office of IT Schedule Contract Operations at the US General Services Administration, Mr. Jose Arrieta, disclosed at the 20 Sep ACT-IAC (American Council for Technology and Industry Advisory Council) Forum that its organization is using blockchain distributed ledger technology to speed up the FASt Lane process for IT Schedule 70 contracts through automation. Two companies, United Solutions (prime contractor) and Sapient Consulting (subcontractor) are developing for FASt Lane a prototype to automate and shorten the time required to perform the contract review process.

The Commercial Customs Operations Advisory Committee, a subcommittee of the U.S. Customs and Border Protection, is working on finding practical ways Blockchain could be implemented in its duties.[1]

Companies have supposedly been suggesting blockchain-based currency solutions in the following two countries:

 

e-Dinar, Tunisia's national currency, was the first state currency using blockchain technology.

eCFA is Senegal's blockchain-based national digital currency.

Some countries, especially Australia, are providing keynote participation in identify the various technical issues associated with developing, governing and using blockchains:

 

In April 2016 Standards Australia submitted a New Field of Technical Activity (NFTA) proposal on behalf of Australia for the International Organization for Standardization (ISO) to consider developing standards to support blockchain technology. The proposal for an NFTA to the ISO was intended to establish a new ISO technical committee for blockchain. The new committee would be responsible for supporting innovation and competition by covering blockchain standards topics including interoperability, terminology, privacy, security and auditing.[99] There have been several media releases[100] supporting blockchain integration to Australian businesses.

Banks

Don Tapscott conducted a two-year research project exploring how blockchain technology can securely move and store host "money, titles, deeds, music, art, scientific discoveries, intellectual property, and even votes".. Furthermore, major portions of the financial industry are implementing distributed ledgers for use in banking, and according to a September 2016 IBM study, this is occurring faster than expected.

 

Banks are interested in this technology because it has potential to speed up back office settlement systems.

 

Banks such as UBS are opening new research labs dedicated to blockchain technology in order to explore how blockchain can be used in financial services to increase efficiency and reduce costs.

 

Russia has officially completed its first government-level blockchain implementation. The state-run bank Sberbank announced 20 December 2017 that it is partnering with Russia's Federal Antimonopoly Service (FAS) to implement document transfer and storage via blockchain.

 

Deloitte and ConsenSys announced plans in 2016 to create a digital bank called Project ConsenSys.

 

R3 connects 42 banks to distributed ledgers built by Ethereum, Chain.com, Intel, IBM and Monax.

 

A Swiss industry consortium, including Swisscom, the Zurich Cantonal Bank and the Swiss stock exchange, is prototyping over-the-counter asset trading on a blockchain-based Ethereum technology.

 

Other financial companies.

The credit and debits payments company MasterCard has added three blockchain-based APIs for programmers to use in developing both person-to-person (P2P) and business-to-business (B2B) payment systems.

 

CLS Group is using blockchain technology to expand the number of currency trade deals it can settle.

 

VISA payment systems, Mastercard,Unionpay and SWIFT have announced the development and plans for using blockchain technology.

 

Prime Shipping Foundation is using blockchain technology to address issues related to the payments in the shipping industry.

 

Other uses

Blockchain technology can be used to create a permanent, public, transparent ledger system for compiling data on sales, storing rights data by authenticating copyright registration,[116] and tracking digital use and payments to content creators, such as musicians. In 2017, IBM partnered with ASCAP and PRS for Music to adopt blockchain technology in music distribution.Imogen Heap's Mycelia service, which allows managers to use a blockchain for tracking high-value parts moving through a supply chain, was launched as a concept in July 2016. Everledger is one of the inaugural clients of IBM's blockchain-based tracking service.

 

Kodak announced plans in 2018 to launch a digital token system for photograph copyright recording.

 

Another example where smart contracts are used is in the music industry. Every time a dj mix is played, the smart contracts attached to the dj mix pays the artists almost instantly.

 

An application has been suggested for securing the spectrum sharing for wireless networks.

 

New distribution methods are available for the insurance industry such as peer-to-peer insurance, parametric insurance and microinsurance following the adoption of blockchain.The sharing economy and IoT are also set to benefit from blockchains because they involve many collaborating peers.Online voting is another application of the blockchain. Blockchains are being used to develop information systems for medical records, which increases interoperability. In theory, legacy disparate systems can be completely replaced by blockchains.Blockchains are being developed for data storage, publishing texts and identifying the origin of digital art. Blockchains facilitate users could take ownership of game assets (digital assets),an example of this is Cryptokitties.

 

Notable non-cryptocurrency designs include:

 

Steemit – a blogging/social networking website and a cryptocurrency

Hyperledger – a cross-industry collaborative effort from the Linux Foundation to support blockchain-based distributed ledgers, with projects under this initiative including Hyperledger Burrow (by Monax) and Hyperledger Fabric (spearheaded by IBM)

Counterparty – an open source financial platform for creating peer-to-peer financial applications on the bitcoin blockchain

Quorum – a permissionable private blockchain by JPMorgan Chase with private storage, used for contract applications

Bitnation – a decentralized borderless "voluntary nation" establishing a jurisdiction of contracts and rules, based on Ethereum

Factom, a distributed registry

Tezos, decentralized voting.

Microsoft Visual Studio is making the Ethereum Solidity language available to application developers.

 

IBM offers a cloud blockchain service based on the open source Hyperledger Fabric project

 

Oracle Cloud offers Blockchain Cloud Service based on Hyperledger Fabric. Oracle has joined the Hyperledger consortium.

 

In August 2016, a research team at the Technical University of Munich published a research document about how blockchains may disrupt industries. They analyzed the venture funding that went into blockchain ventures. Their research shows that $1.55 billion went into startups with an industry focus on finance and insurance, information and communication, and professional services. High startup density was found in the USA, UK and Canada.

 

ABN Amro announced a project in real estate to facilitate the sharing and recording of real estate transactions, and a second project in partnership with the Port of Rotterdam to develop logistics tools.

 

Academic research

 

Blockchain panel discussion at the first IEEE Computer Society TechIgnite conference

In October 2014, the MIT Bitcoin Club, with funding from MIT alumni, provided undergraduate students at the Massachusetts Institute of Technology access to $100 of bitcoin. The adoption rates, as studied by Catalini and Tucker (2016), revealed that when people who typically adopt technologies early are given delayed access, they tend to reject the technology.

 

Journals

 

In September 2015, the first peer-reviewed academic journal dedicated to cryptocurrency and blockchain technology research, Ledger, was announced. The inaugural issue was published in December 2016. The journal covers aspects of mathematics, computer science, engineering, law, economics and philosophy that relate to cryptocurrencies such as bitcoin. There are also research platforms like Strategic coin that offer research for the blockchain and crypto space.

 

The journal encourages authors to digitally sign a file hash of submitted papers, which will then be timestamped into the bitcoin blockchain. Authors are also asked to include a personal bitcoin address in the first page of their papers.

 

Predictions

A World Economic Forum report from September 2015 predicted that by 2025 ten percent of global GDP would be stored on blockchains technology.

 

In early 2017, Harvard Business School professors Marco Iansiti and Karim R. Lakhani said the blockchain is not a disruptive technology that undercuts the cost of an existing business model, but is a foundational technology that "has the potential to create new foundations for our economic and social systems". They further predicted that, while foundational innovations can have enormous impact, "It will take decades for blockchain to seep into our economic and social infrastructure."

 

en.wikipedia.org/wiki/Blockchain

This is two iterations of a substitution where the prototile shapes are defined by cutting a regular polygon along all of its diagonals. Higher-order polygons will involve more types of tiles; pentagons use 3 tile types, heptagons use 7 tile types, nonagons use 14.

 

I think the same method should be extensible to even-numbered polygons, but have run out of drawing time today. Stay tuned!

Prototype of the Mercury, an infinitely extensible, open camera system that I developed over the past two years, with some help from others. This one is shown configured for 6x9 medium format.

Mayo: Mascotas

#‎reto12meses12temas

---

May: Pets

‪#‎12months12topicschallenge‬

======

Carmen Cabrera © All Rights Reserved

 

More About me.

Sans fil bâton YUNTENG 1288 extensible Manfrotto rechargeable Bluetooth à distance l’obturateur pour Xiaomi yi action appareil photo et téléphone

Le paquet contient:

 

1 x YUNTENG 1288 extensible Handheld Manfrotto

...

 

telephone.pascherenchine.com/products/sans-fil-selfie-bat...

This is three iterations of a substitution where the prototile shapes are defined by cutting a polygon along all of its diagonals. Higher-order polygons will involve more types of tiles; pentagons use 3 tile types, heptagons use 7 tile types, nonagons use 14.

 

I think the same method should be extensible to even-numbered polygons, but have run out of drawing time today. Stay tuned!

Prototype of the Mercury, an infinitely extensible, open camera system that I developed over the past two years, with some help from others. This one is shown configured for 6x9 medium format.

East Jesus is an experimental, habitable, extensible artwork in progress since 2006 begun by the late Charles Stephen Russell in Slab City, California. The inhabitants of East Jesus and offsite members provide a refuge for artists, musicians, survivalists, writers, scientists, and laymen. They are dedicated to providing a working model of an improbable improvised community. Completely self-contained and run entirely on solar power, East Jesus attempts to use and recycle every bit of consumable trash.

(from Wikipedia)

An American White Pelican swimming quietly on the reflective surface of the lake. The vibrant orange bill and the crisp white plumage contrast sharply with the deep blue, rippled water.

 

I photographed this striking bird during an early morning visit to Sally Jones Lake at the Sequoyah National Wildlife Refuge in Oklahoma. The calm, late November light provided the perfect setting for a close-up.

 

This large species is easily recognized by its long bill and extensible pouch, which it uses to scoop up fish while swimming. Unlike its brown relatives, the American White Pelican does not plunge-dive for food.

Filaire Manfrotto extensible Handheld bâton pôle support avec bouton à distance sur le bâton Top vendeur dans le marché d’aujourd’hui A £ 49.99 Maintenant 6.79 Mai n...

 

telephone.pascherenchine.com/products/new-manfrotto-cable...

PHILIPPINE SEA (Sep. 26, 2021) Mineman 2nd Class Alan Molina, right, from Summit, Illinois, and Mineman 3rd Class Brendan Riemrlanglois, from Crandon, Wisconsin, prepare an 11-meter rigid hull inflatable boat to be hoisted during a twin boom extensible crane training evolution in the mission bay aboard Independence-variant littoral combat ship USS Charleston (LCS 18). Charleston, part of Destroyer Squadron 7, is on a rotational deployment, operating in the U.S. 7th Fleet to enhance interoperability with partners and serve as a ready-response force in support of free and open Indo-Pacific region. (U.S. Navy photo by Mass Communication Specialist 2nd Class Ryan M. Breeden)

Jellyfish, also known sea jellies, are the medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria.

 

Jellyfish are mainly free-swimming marine animals with umbrella-shaped bells and trailing tentacles, although a few are anchored to the seabed by stalks rather than being mobile. The bell can pulsate to provide propulsion for highly efficient locomotion. The tentacles are armed with stinging cells and may be used to capture prey and defend against predators. Jellyfish have a complex life cycle. The medusa is normally the sexual phase, which produces planula larvae; these then disperse widely and enter a sedentary polyp phase, before reaching sexual maturity.

 

Jellyfish are found all over the world, from surface waters to the deep sea. Scyphozoans (the "true jellyfish") are exclusively marine, but some hydrozoans with a similar appearance live in freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide. The medusae of most species are fast-growing, and mature within a few months then die soon after breeding, but the polyp stage, attached to the seabed, may be much more long-lived. Jellyfish have been in existence for at least 500 million years, and possibly 700 million years or more, making them the oldest multi-organ animal group.

 

Jellyfish are eaten by humans in certain cultures. They are considered a delicacy in some Asian countries, where species in the Rhizostomeae order are pressed and salted to remove excess water. Australian researchers have described them as a "perfect food": sustainable and protein-rich but relatively low in food energy.

 

They are also used in research, where the green fluorescent protein used by some species to cause bioluminescence has been adapted as a fluorescent marker for genes inserted into other cells or organisms.

 

The stinging cells used by jellyfish to subdue their prey can injure humans. Thousands of swimmers worldwide are stung every year, with effects ranging from mild discomfort to serious injury or even death. When conditions are favourable, jellyfish can form vast swarms, which can be responsible for damage to fishing gear by filling fishing nets, and sometimes clog the cooling systems of power and desalination plants which draw their water from the sea.

  

Names

The name jellyfish, in use since 1796, has traditionally been applied to medusae and all similar animals including the comb jellies (ctenophores, another phylum). The term jellies or sea jellies is more recent, having been introduced by public aquaria in an effort to avoid use of the word "fish" with its modern connotation of an animal with a backbone, though shellfish, cuttlefish and starfish are not vertebrates either. In scientific literature, "jelly" and "jellyfish" have been used interchangeably. Many sources refer to only scyphozoans as "true jellyfish".

 

A group of jellyfish is called a "smack" or a "smuck".

 

Definition

The term jellyfish broadly corresponds to medusae, that is, a life-cycle stage in the Medusozoa. The American evolutionary biologist Paulyn Cartwright gives the following general definition:

 

Typically, medusozoan cnidarians have a pelagic, predatory jellyfish stage in their life cycle; staurozoans are the exceptions [as they are stalked].

 

The Merriam-Webster dictionary defines jellyfish as follows:

 

A free-swimming marine coelenterate that is the sexually reproducing form of a hydrozoan or scyphozoan and has a nearly transparent saucer-shaped body and extensible marginal tentacles studded with stinging cells.

 

Given that jellyfish is a common name, its mapping to biological groups is inexact. Some authorities have called the comb jellies and certain salps jellyfish, though other authorities state that neither of these are jellyfish, which they consider should be limited to certain groups within the medusozoa.

 

The non-medusozoan clades called jellyfish by some but not all authorities (both agreeing and disagreeing citations are given in each case) are indicated with on the following cladogram of the animal kingdom:

 

Jellyfish are not a clade, as they include most of the Medusozoa, barring some of the Hydrozoa. The medusozoan groups included by authorities are indicated on the following phylogenetic tree by the presence of citations. Names of included jellyfish, in English where possible, are shown in boldface; the presence of a named and cited example indicates that at least that species within its group has been called a jellyfish.

 

Taxonomy

The subphylum Medusozoa includes all cnidarians with a medusa stage in their life cycle. The basic cycle is egg, planula larva, polyp, medusa, with the medusa being the sexual stage. The polyp stage is sometimes secondarily lost. The subphylum include the major taxa, Scyphozoa (large jellyfish), Cubozoa (box jellyfish) and Hydrozoa (small jellyfish), and excludes Anthozoa (corals and sea anemones). This suggests that the medusa form evolved after the polyps. Medusozoans have tetramerous symmetry, with parts in fours or multiples of four.

 

The four major classes of medusozoan Cnidaria are:

Scyphozoa are sometimes called true jellyfish, though they are no more truly jellyfish than the others listed here. They have tetra-radial symmetry. Most have tentacles around the outer margin of the bowl-shaped bell, and long, oral arms around the mouth in the center of the subumbrella.

Cubozoa (box jellyfish) have a (rounded) box-shaped bell, and their velarium assists them to swim more quickly. Box jellyfish may be related more closely to scyphozoan jellyfish than either are to the Hydrozoa.

Hydrozoa medusae also have tetra-radial symmetry, nearly always have a velum (diaphragm used in swimming) attached just inside the bell margin, do not have oral arms, but a much smaller central stalk-like structure, the manubrium, with terminal mouth opening, and are distinguished by the absence of cells in the mesoglea. Hydrozoa show great diversity of lifestyle; some species maintain the polyp form for their entire life and do not form medusae at all (such as Hydra, which is hence not considered a jellyfish), and a few are entirely medusal and have no polyp form.

Staurozoa (stalked jellyfish) are characterized by a medusa form that is generally sessile, oriented upside down and with a stalk emerging from the apex of the "calyx" (bell), which attaches to the substrate. At least some Staurozoa also have a polyp form that alternates with the medusoid portion of the life cycle. Until recently, Staurozoa were classified within the Scyphozoa.

There are over 200 species of Scyphozoa, about 50 species of Staurozoa, about 50 species of Cubozoa, and the Hydrozoa includes about 1000–1500 species that produce medusae, but many more species that do not.

 

Fossil history

Since jellyfish have no hard parts, fossils are rare. The oldest unambiguous fossil of a free-swimming medusa is Burgessomedusa from the mid Cambrian Burgess Shale of Canada, which is likely either a stem group of box jellyfish (Cubozoa) or Acraspeda (the clade including Staurozoa, Cubozoa, and Scyphozoa). Other claimed records from the Cambrian of China and Utah in the United States are uncertain, and possibly represent ctenophores instead.

 

Anatomy

The main feature of a true jellyfish is the umbrella-shaped bell. This is a hollow structure consisting of a mass of transparent jelly-like matter known as mesoglea, which forms the hydrostatic skeleton of the animal. 95% or more of the mesogloea consists of water, but it also contains collagen and other fibrous proteins, as well as wandering amoebocytes which can engulf debris and bacteria. The mesogloea is bordered by the epidermis on the outside and the gastrodermis on the inside. The edge of the bell is often divided into rounded lobes known as lappets, which allow the bell to flex. In the gaps or niches between the lappets are dangling rudimentary sense organs known as rhopalia, and the margin of the bell often bears tentacles.

  

Anatomy of a scyphozoan jellyfish

On the underside of the bell is the manubrium, a stalk-like structure hanging down from the centre, with the mouth, which also functions as the anus, at its tip. There are often four oral arms connected to the manubrium, streaming away into the water below. The mouth opens into the gastrovascular cavity, where digestion takes place and nutrients are absorbed. This is subdivided by four thick septa into a central stomach and four gastric pockets. The four pairs of gonads are attached to the septa, and close to them four septal funnels open to the exterior, perhaps supplying good oxygenation to the gonads. Near the free edges of the septa, gastric filaments extend into the gastric cavity; these are armed with nematocysts and enzyme-producing cells and play a role in subduing and digesting the prey. In some scyphozoans, the gastric cavity is joined to radial canals which branch extensively and may join a marginal ring canal. Cilia in these canals circulate the fluid in a regular direction.

  

Discharge mechanism of a nematocyst

The box jellyfish is largely similar in structure. It has a squarish, box-like bell. A short pedalium or stalk hangs from each of the four lower corners. One or more long, slender tentacles are attached to each pedalium. The rim of the bell is folded inwards to form a shelf known as a velarium which restricts the bell's aperture and creates a powerful jet when the bell pulsates, allowing box jellyfish to swim faster than true jellyfish. Hydrozoans are also similar, usually with just four tentacles at the edge of the bell, although many hydrozoans are colonial and may not have a free-living medusal stage. In some species, a non-detachable bud known as a gonophore is formed that contains a gonad but is missing many other medusal features such as tentacles and rhopalia. Stalked jellyfish are attached to a solid surface by a basal disk, and resemble a polyp, the oral end of which has partially developed into a medusa with tentacle-bearing lobes and a central manubrium with four-sided mouth.

 

Most jellyfish do not have specialized systems for osmoregulation, respiration and circulation, and do not have a central nervous system. Nematocysts, which deliver the sting, are located mostly on the tentacles; true jellyfish also have them around the mouth and stomach. Jellyfish do not need a respiratory system because sufficient oxygen diffuses through the epidermis. They have limited control over their movement, but can navigate with the pulsations of the bell-like body; some species are active swimmers most of the time, while others largely drift. The rhopalia contain rudimentary sense organs which are able to detect light, water-borne vibrations, odour and orientation. A loose network of nerves called a "nerve net" is located in the epidermis. Although traditionally thought not to have a central nervous system, nerve net concentration and ganglion-like structures could be considered to constitute one in most species. A jellyfish detects stimuli, and transmits impulses both throughout the nerve net and around a circular nerve ring, to other nerve cells. The rhopalial ganglia contain pacemaker neurones which control swimming rate and direction.

 

In many species of jellyfish, the rhopalia include ocelli, light-sensitive organs able to tell light from dark. These are generally pigment spot ocelli, which have some of their cells pigmented. The rhopalia are suspended on stalks with heavy crystals at one end, acting like gyroscopes to orient the eyes skyward. Certain jellyfish look upward at the mangrove canopy while making a daily migration from mangrove swamps into the open lagoon, where they feed, and back again.

 

Box jellyfish have more advanced vision than the other groups. Each individual has 24 eyes, two of which are capable of seeing colour, and four parallel information processing areas that act in competition, supposedly making them one of the few kinds of animal to have a 360-degree view of its environment.

 

Box jellyfish eye

The study of jellyfish eye evolution is an intermediary to a better understanding of how visual systems evolved on Earth. Jellyfish exhibit immense variation in visual systems ranging from photoreceptive cell patches seen in simple photoreceptive systems to more derived complex eyes seen in box jellyfish. Major topics of jellyfish visual system research (with an emphasis on box jellyfish) include: the evolution of jellyfish vision from simple to complex visual systems), the eye morphology and molecular structures of box jellyfish (including comparisons to vertebrate eyes), and various uses of vision including task-guided behaviors and niche specialization.

 

Evolution

Experimental evidence for photosensitivity and photoreception in cnidarians antecedes the mid 1900s, and a rich body of research has since covered evolution of visual systems in jellyfish. Jellyfish visual systems range from simple photoreceptive cells to complex image-forming eyes. More ancestral visual systems incorporate extraocular vision (vision without eyes) that encompass numerous receptors dedicated to single-function behaviors. More derived visual systems comprise perception that is capable of multiple task-guided behaviors.

 

Although they lack a true brain, cnidarian jellyfish have a "ring" nervous system that plays a significant role in motor and sensory activity. This net of nerves is responsible for muscle contraction and movement and culminates the emergence of photosensitive structures. Across Cnidaria, there is large variation in the systems that underlie photosensitivity. Photosensitive structures range from non-specialized groups of cells, to more "conventional" eyes similar to those of vertebrates. The general evolutionary steps to develop complex vision include (from more ancestral to more derived states): non-directional photoreception, directional photoreception, low-resolution vision, and high-resolution vision. Increased habitat and task complexity has favored the high-resolution visual systems common in derived cnidarians such as box jellyfish.

 

Basal visual systems observed in various cnidarians exhibit photosensitivity representative of a single task or behavior. Extraocular photoreception (a form of non-directional photoreception), is the most basic form of light sensitivity and guides a variety of behaviors among cnidarians. It can function to regulate circadian rhythm (as seen in eyeless hydrozoans) and other light-guided behaviors responsive to the intensity and spectrum of light. Extraocular photoreception can function additionally in positive phototaxis (in planula larvae of hydrozoans), as well as in avoiding harmful amounts of UV radiation via negative phototaxis. Directional photoreception (the ability to perceive direction of incoming light) allows for more complex phototactic responses to light, and likely evolved by means of membrane stacking. The resulting behavioral responses can range from guided spawning events timed by moonlight to shadow responses for potential predator avoidance. Light-guided behaviors are observed in numerous scyphozoans including the common moon jelly, Aurelia aurita, which migrates in response to changes in ambient light and solar position even though they lack proper eyes.

 

The low-resolution visual system of box jellyfish is more derived than directional photoreception, and thus box jellyfish vision represents the most basic form of true vision in which multiple directional photoreceptors combine to create the first imaging and spatial resolution. This is different from the high-resolution vision that is observed in camera or compound eyes of vertebrates and cephalopods that rely on focusing optics. Critically, the visual systems of box jellyfish are responsible for guiding multiple tasks or behaviors in contrast to less derived visual systems in other jellyfish that guide single behavioral functions. These behaviors include phototaxis based on sunlight (positive) or shadows (negative), obstacle avoidance, and control of swim-pulse rate.

 

Box jellyfish possess "proper eyes" (similar to vertebrates) that allow them to inhabit environments that lesser derived medusae cannot. In fact, they are considered the only class in the clade Medusozoa that have behaviors necessitating spatial resolution and genuine vision. However, the lens in their eyes are more functionally similar to cup-eyes exhibited in low-resolution organisms, and have very little to no focusing capability. The lack of the ability to focus is due to the focal length exceeding the distance to the retina, thus generating unfocused images and limiting spatial resolution. The visual system is still sufficient for box jellyfish to produce an image to help with tasks such as object avoidance.

 

Utility as a model organism

Box jellyfish eyes are a visual system that is sophisticated in numerous ways. These intricacies include the considerable variation within the morphology of box jellyfishes' eyes (including their task/behavior specification), and the molecular makeup of their eyes including: photoreceptors, opsins, lenses, and synapses. The comparison of these attributes to more derived visual systems can allow for a further understanding of how the evolution of more derived visual systems may have occurred, and puts into perspective how box jellyfish can play the role as an evolutionary/developmental model for all visual systems.

 

Characteristics

Box jellyfish visual systems are both diverse and complex, comprising multiple photosystems. There is likely considerable variation in visual properties between species of box jellyfish given the significant inter-species morphological and physiological variation. Eyes tend to differ in size and shape, along with number of receptors (including opsins), and physiology across species of box jellyfish.

 

Box jellyfish have a series of intricate lensed eyes that are similar to those of more derived multicellular organisms such as vertebrates. Their 24 eyes fit into four different morphological categories. These categories consist of two large, morphologically different medial eyes (a lower and upper lensed eye) containing spherical lenses, a lateral pair of pigment slit eyes, and a lateral pair of pigment pit eyes. The eyes are situated on rhopalia (small sensory structures) which serve sensory functions of the box jellyfish and arise from the cavities of the exumbrella (the surface of the body) on the side of the bells of the jellyfish. The two large eyes are located on the mid-line of the club and are considered complex because they contain lenses. The four remaining eyes lie laterally on either side of each rhopalia and are considered simple. The simple eyes are observed as small invaginated cups of epithelium that have developed pigmentation. The larger of the complex eyes contains a cellular cornea created by a mono ciliated epithelium, cellular lens, homogenous capsule to the lens, vitreous body with prismatic elements, and a retina of pigmented cells. The smaller of the complex eyes is said to be slightly less complex given that it lacks a capsule but otherwise contains the same structure as the larger eye.

 

Box jellyfish have multiple photosystems that comprise different sets of eyes. Evidence includes immunocytochemical and molecular data that show photopigment differences among the different morphological eye types, and physiological experiments done on box jellyfish to suggest behavioral differences among photosystems. Each individual eye type constitutes photosystems that work collectively to control visually guided behaviors.

 

Box jellyfish eyes primarily use c-PRCs (ciliary photoreceptor cells) similar to that of vertebrate eyes. These cells undergo phototransduction cascades (process of light absorption by photoreceptors) that are triggered by c-opsins. Available opsin sequences suggest that there are two types of opsins possessed by all cnidarians including an ancient phylogenetic opsin, and a sister ciliary opsin to the c-opsins group. Box jellyfish could have both ciliary and cnidops (cnidarian opsins), which is something not previously believed to appear in the same retina. Nevertheless, it is not entirely evident whether cnidarians possess multiple opsins that are capable of having distinctive spectral sensitivities.

 

Comparison with other organisms

Comparative research on genetic and molecular makeup of box jellyfishes' eyes versus more derived eyes seen in vertebrates and cephalopods focuses on: lenses and crystallin composition, synapses, and Pax genes and their implied evidence for shared primordial (ancestral) genes in eye evolution.

 

Box jellyfish eyes are said to be an evolutionary/developmental model of all eyes based on their evolutionary recruitment of crystallins and Pax genes. Research done on box jellyfish including Tripedalia cystophora has suggested that they possess a single Pax gene, PaxB. PaxB functions by binding to crystallin promoters and activating them. PaxB in situ hybridization resulted in PaxB expression in the lens, retina, and statocysts. These results and the rejection of the prior hypothesis that Pax6 was an ancestral Pax gene in eyes has led to the conclusion that PaxB was a primordial gene in eye evolution, and that the eyes of all organisms likely share a common ancestor.

 

The lens structure of box jellyfish appears very similar to those of other organisms, but the crystallins are distinct in both function and appearance. Weak reactions were seen within the sera and there were very weak sequence similarities within the crystallins among vertebrate and invertebrate lenses. This is likely due to differences in lower molecular weight proteins and the subsequent lack of immunological reactions with antisera that other organisms' lenses exhibit.

 

All four of the visual systems of box jellyfish species investigated with detail (Carybdea marsupialis, Chiropsalmus quadrumanus, Tamoya haplonema and Tripedalia cystophora) have invaginated synapses, but only in the upper and lower lensed eyes. Different densities were found between the upper and lower lenses, and between species. Four types of chemical synapses have been discovered within the rhopalia which could help in understanding neural organization including: clear unidirectional, dense-core unidirectional, clear bidirectional, and clear and dense-core bidirectional. The synapses of the lensed eyes could be useful as markers to learn more about the neural circuit in box jellyfish retinal areas.

 

Evolution as a response to natural stimuli

The primary adaptive responses to environmental variation observed in box jellyfish eyes include pupillary constriction speeds in response to light environments, as well as photoreceptor tuning and lens adaptations to better respond to shifts between light environments and darkness. Interestingly, some box jellyfish species' eyes appear to have evolved more focused vision in response to their habitat.

 

Pupillary contraction appears to have evolved in response to variation in the light environment across ecological niches across three species of box jellyfish (Chironex fleckeri, Chiropsella bronzie, and Carukia barnesi). Behavioral studies suggest that faster pupil contraction rates allow for greater object avoidance, and in fact, species with more complex habitats exhibit faster rates. Ch. bronzie inhabit shallow beach fronts that have low visibility and very few obstacles, thus, faster pupil contraction in response to objects in their environment is not important. Ca. barnesi and Ch. fleckeri are found in more three-dimensionally complex environments like mangroves with an abundance of natural obstacles, where faster pupil contraction is more adaptive. Behavioral studies support the idea that faster pupillary contraction rates assist with obstacle avoidance as well as depth adjustments in response to differing light intensities.

 

Light/dark adaptation via pupillary light reflexes is an additional form of an evolutionary response to the light environment. This relates to the pupil's response to shifts between light intensity (generally from sunlight to darkness). In the process of light/dark adaptation, the upper and lower lens eyes of different box jellyfish species vary in specific function. The lower lens-eyes contain pigmented photoreceptors and long pigment cells with dark pigments that migrate on light/dark adaptation, while the upper-lens eyes play a concentrated role in light direction and phototaxis given that they face upward towards the water surface (towards the sun or moon). The upper lens of Ch. bronzie does not exhibit any considerable optical power while Tr. cystophora (a box jellyfish species that tends to live in mangroves) does. The ability to use light to visually guide behavior is not of as much importance to Ch. bronzie as it is to species in more obstacle-filled environments. Differences in visually guided behavior serve as evidence that species that share the same number and structure of eyes can exhibit differences in how they control behavior.

 

Largest and smallest

Jellyfish range from about one millimeter in bell height and diameter, to nearly 2 metres (6+1⁄2 ft) in bell height and diameter; the tentacles and mouth parts usually extend beyond this bell dimension.

 

The smallest jellyfish are the peculiar creeping jellyfish in the genera Staurocladia and Eleutheria, which have bell disks from 0.5 millimetres (1⁄32 in) to a few millimeters in diameter, with short tentacles that extend out beyond this, which these jellyfish use to move across the surface of seaweed or the bottoms of rocky pools; many of these tiny creeping jellyfish cannot be seen in the field without a hand lens or microscope. They can reproduce asexually by fission (splitting in half). Other very small jellyfish, which have bells about one millimeter, are the hydromedusae of many species that have just been released from their parent polyps; some of these live only a few minutes before shedding their gametes in the plankton and then dying, while others will grow in the plankton for weeks or months. The hydromedusae Cladonema radiatum and Cladonema californicum are also very small, living for months, yet never growing beyond a few mm in bell height and diameter.

 

The lion's mane jellyfish, Cyanea capillata, was long-cited as the largest jellyfish, and arguably the longest animal in the world, with fine, thread-like tentacles that may extend up to 36.5 m (119 ft 9 in) long (though most are nowhere near that large). They have a moderately painful, but rarely fatal, sting. The increasingly common giant Nomura's jellyfish, Nemopilema nomurai, found in some, but not all years in the waters of Japan, Korea and China in summer and autumn is another candidate for "largest jellyfish", in terms of diameter and weight, since the largest Nomura's jellyfish in late autumn can reach 2 m (6 ft 7 in) in bell (body) diameter and about 200 kg (440 lb) in weight, with average specimens frequently reaching 0.9 m (2 ft 11 in) in bell diameter and about 150 kg (330 lb) in weight. The large bell mass of the giant Nomura's jellyfish can dwarf a diver and is nearly always much greater than the Lion's Mane, whose bell diameter can reach 1 m (3 ft 3 in).

 

The rarely encountered deep-sea jellyfish Stygiomedusa gigantea is another candidate for "largest jellyfish", with its thick, massive bell up to 100 cm (3 ft 3 in) wide, and four thick, "strap-like" oral arms extending up to 6 m (19+1⁄2 ft) in length, very different from the typical fine, threadlike tentacles that rim the umbrella of more-typical-looking jellyfish, including the Lion's Mane.

 

Desmonema glaciale, which lives in the Antarctic region, can reach a very large size (several meters). Purple-striped jelly (Chrysaora colorata) can also be extremely long (up to 15 feet).

 

Life history and behavior

Life cycle

Jellyfish have a complex life cycle which includes both sexual and asexual phases, with the medusa being the sexual stage in most instances. Sperm fertilize eggs, which develop into larval planulae, become polyps, bud into ephyrae and then transform into adult medusae. In some species certain stages may be skipped.

 

Upon reaching adult size, jellyfish spawn regularly if there is a sufficient supply of food. In most species, spawning is controlled by light, with all individuals spawning at about the same time of day; in many instances this is at dawn or dusk. Jellyfish are usually either male or female (with occasional hermaphrodites). In most cases, adults release sperm and eggs into the surrounding water, where the unprotected eggs are fertilized and develop into larvae. In a few species, the sperm swim into the female's mouth, fertilizing the eggs within her body, where they remain during early development stages. In moon jellies, the eggs lodge in pits on the oral arms, which form a temporary brood chamber for the developing planula larvae.

 

The planula is a small larva covered with cilia. When sufficiently developed, it settles onto a firm surface and develops into a polyp. The polyp generally consists of a small stalk topped by a mouth that is ringed by upward-facing tentacles. The polyps resemble those of closely related anthozoans, such as sea anemones and corals. The jellyfish polyp may be sessile, living on the bottom, boat hulls or other substrates, or it may be free-floating or attached to tiny bits of free-living plankton or rarely, fish or other invertebrates. Polyps may be solitary or colonial. Most polyps are only millimetres in diameter and feed continuously. The polyp stage may last for years.

 

After an interval and stimulated by seasonal or hormonal changes, the polyp may begin reproducing asexually by budding and, in the Scyphozoa, is called a segmenting polyp, or a scyphistoma. Budding produces more scyphistomae and also ephyrae. Budding sites vary by species; from the tentacle bulbs, the manubrium (above the mouth), or the gonads of hydromedusae. In a process known as strobilation, the polyp's tentacles are reabsorbed and the body starts to narrow, forming transverse constrictions, in several places near the upper extremity of the polyp. These deepen as the constriction sites migrate down the body, and separate segments known as ephyra detach. These are free-swimming precursors of the adult medusa stage, which is the life stage that is typically identified as a jellyfish. The ephyrae, usually only a millimeter or two across initially, swim away from the polyp and grow. Limnomedusae polyps can asexually produce a creeping frustule larval form, which crawls away before developing into another polyp. A few species can produce new medusae by budding directly from the medusan stage. Some hydromedusae reproduce by fission.

 

Lifespan

Little is known of the life histories of many jellyfish as the places on the seabed where the benthic forms of those species live have not been found. However, an asexually reproducing strobila form can sometimes live for several years, producing new medusae (ephyra larvae) each year.

 

An unusual species, Turritopsis dohrnii, formerly classified as Turritopsis nutricula, might be effectively immortal because of its ability under certain circumstances to transform from medusa back to the polyp stage, thereby escaping the death that typically awaits medusae post-reproduction if they have not otherwise been eaten by some other organism. So far this reversal has been observed only in the laboratory.

 

Locomotion

Jellyfish locomotion is highly efficient. Muscles in the jellylike bell contract, setting up a start vortex and propelling the animal. When the contraction ends, the bell recoils elastically, creating a stop vortex with no extra energy input.

Using the moon jelly Aurelia aurita as an example, jellyfish have been shown to be the most energy-efficient swimmers of all animals. They move through the water by radially expanding and contracting their bell-shaped bodies to push water behind them. They pause between the contraction and expansion phases to create two vortex rings. Muscles are used for the contraction of the body, which creates the first vortex and pushes the animal forward, but the mesoglea is so elastic that the expansion is powered exclusively by relaxing the bell, which releases the energy stored from the contraction. Meanwhile, the second vortex ring starts to spin faster, sucking water into the bell and pushing against the centre of the body, giving a secondary and "free" boost forward. The mechanism, called passive energy recapture, only works in relatively small jellyfish moving at low speeds, allowing the animal to travel 30 percent farther on each swimming cycle. Jellyfish achieved a 48 percent lower cost of transport (food and oxygen intake versus energy spent in movement) than other animals in similar studies. One reason for this is that most of the gelatinous tissue of the bell is inactive, using no energy during swimming.

 

Ecology

Diet

Jellyfish are, like other cnidarians, generally carnivorous (or parasitic), feeding on planktonic organisms, crustaceans, small fish, fish eggs and larvae, and other jellyfish, ingesting food and voiding undigested waste through the mouth. They hunt passively using their tentacles as drift lines, or sink through the water with their tentacles spread widely; the tentacles, which contain nematocysts to stun or kill the prey, may then flex to help bring it to the mouth. Their swimming technique also helps them to capture prey; when their bell expands it sucks in water which brings more potential prey within reach of the tentacles.

 

A few species such as Aglaura hemistoma are omnivorous, feeding on microplankton which is a mixture of zooplankton and phytoplankton (microscopic plants) such as dinoflagellates. Others harbour mutualistic algae (Zooxanthellae) in their tissues; the spotted jellyfish (Mastigias papua) is typical of these, deriving part of its nutrition from the products of photosynthesis, and part from captured zooplankton. The upside-down jellyfish (Cassiopea andromeda) also has a symbiotic relationship with microalgae, but captures tiny animals to supplement their diet. This is done by releasing tiny balls of living cells composed of mesoglea. These use cilia to drive them through water and stinging cells which stun the prey. The blobs also seems to have digestive capabilities.

 

Predation

Other species of jellyfish are among the most common and important jellyfish predators. Sea anemones may eat jellyfish that drift into their range. Other predators include tunas, sharks, swordfish, sea turtles and penguins. Jellyfish washed up on the beach are consumed by foxes, other terrestrial mammals and birds. In general however, few animals prey on jellyfish; they can broadly be considered to be top predators in the food chain. Once jellyfish have become dominant in an ecosystem, for example through overfishing which removes predators of jellyfish larvae, there may be no obvious way for the previous balance to be restored: they eat fish eggs and juvenile fish, and compete with fish for food, preventing fish stocks from recovering.

 

Symbiosis

Some small fish are immune to the stings of the jellyfish and live among the tentacles, serving as bait in a fish trap; they are safe from potential predators and are able to share the fish caught by the jellyfish. The cannonball jellyfish has a symbiotic relationship with ten different species of fish, and with the longnose spider crab, which lives inside the bell, sharing the jellyfish's food and nibbling its tissues.

 

Main article: Jellyfish bloom

Jellyfish form large masses or blooms in certain environmental conditions of ocean currents, nutrients, sunshine, temperature, season, prey availability, reduced predation and oxygen concentration. Currents collect jellyfish together, especially in years with unusually high populations. Jellyfish can detect marine currents and swim against the current to congregate in blooms. Jellyfish are better able to survive in nutrient-rich, oxygen-poor water than competitors, and thus can feast on plankton without competition. Jellyfish may also benefit from saltier waters, as saltier waters contain more iodine, which is necessary for polyps to turn into jellyfish. Rising sea temperatures caused by climate change may also contribute to jellyfish blooms, because many species of jellyfish are able to survive in warmer waters. Increased nutrients from agricultural or urban runoff with nutrients including nitrogen and phosphorus compounds increase the growth of phytoplankton, causing eutrophication and algal blooms. When the phytoplankton die, they may create dead zones, so-called because they are hypoxic (low in oxygen). This in turn kills fish and other animals, but not jellyfish, allowing them to bloom. Jellyfish populations may be expanding globally as a result of land runoff and overfishing of their natural predators. Jellyfish are well placed to benefit from disturbance of marine ecosystems. They reproduce rapidly; they prey upon many species, while few species prey on them; and they feed via touch rather than visually, so they can feed effectively at night and in turbid waters. It may be difficult for fish stocks to re-establish themselves in marine ecosystems once they have become dominated by jellyfish, because jellyfish feed on plankton, which includes fish eggs and larvae.

 

As suspected at the turn of this century, jellyfish blooms are increasing in frequency. Between 2013 and 2020 the Mediterranean Science Commission monitored on a weekly basis the frequency of such outbreaks in coastal waters from Morocco to the Black Sea, revealing a relatively high frequency of these blooms nearly all year round, with peaks observed from March to July and often again in the autumn. The blooms are caused by different jellyfish species, depending on their localisation within the Basin: one observes a clear dominance of Pelagia noctiluca and Velella velella outbreaks in the western Mediterranean, of Rhizostoma pulmo and Rhopilema nomadica outbreaks in the eastern Mediterranean, and of Aurelia aurita and Mnemiopsis leidyi outbreaks in the Black Sea.

 

Some jellyfish populations that have shown clear increases in the past few decades are invasive species, newly arrived from other habitats: examples include the Black Sea, Caspian Sea, Baltic Sea, central and eastern Mediterranean, Hawaii, and tropical and subtropical parts of the West Atlantic (including the Caribbean, Gulf of Mexico and Brazil).

 

Jellyfish blooms can have significant impact on community structure. Some carnivorous jellyfish species prey on zooplankton while others graze on primary producers. Reductions in zooplankton and ichthyoplankton due to a jellyfish bloom can ripple through the trophic levels. High-density jellyfish populations can outcompete other predators and reduce fish recruitment. Increased grazing on primary producers by jellyfish can also interrupt energy transfer to higher trophic levels.

 

During blooms, jellyfish significantly alter the nutrient availability in their environment. Blooms require large amounts of available organic nutrients in the water column to grow, limiting availability for other organisms. Some jellyfish have a symbiotic relationship with single-celled dinoflagellates, allowing them to assimilate inorganic carbon, phosphorus, and nitrogen creating competition for phytoplankton. Their large biomass makes them an important source of dissolved and particulate organic matter for microbial communities through excretion, mucus production, and decomposition. The microbes break down the organic matter into inorganic ammonium and phosphate. However, the low carbon availability shifts the process from production to respiration creating low oxygen areas making the dissolved inorganic nitrogen and phosphorus largely unavailable for primary production.

 

These blooms have very real impacts on industries. Jellyfish can outcompete fish by utilizing open niches in over-fished fisheries. Catch of jellyfish can strain fishing gear and lead to expenses relating to damaged gear. Power plants have been shut down due to jellyfish blocking the flow of cooling water. Blooms have also been harmful for tourism, causing a rise in stings and sometimes the closure of beaches.

 

Jellyfish form a component of jelly-falls, events where gelatinous zooplankton fall to the seafloor, providing food for the benthic organisms there. In temperate and subpolar regions, jelly-falls usually follow immediately after a bloom.

 

Habitats

Most jellyfish are marine animals, although a few hydromedusae inhabit freshwater. The best known freshwater example is the cosmopolitan hydrozoan jellyfish, Craspedacusta sowerbii. It is less than an inch (2.5 cm) in diameter, colorless and does not sting. Some jellyfish populations have become restricted to coastal saltwater lakes, such as Jellyfish Lake in Palau. Jellyfish Lake is a marine lake where millions of golden jellyfish (Mastigias spp.) migrate horizontally across the lake daily.

 

Although most jellyfish live well off the ocean floor and form part of the plankton, a few species are closely associated with the bottom for much of their lives and can be considered benthic. The upside-down jellyfish in the genus Cassiopea typically lie on the bottom of shallow lagoons where they sometimes pulsate gently with their umbrella top facing down. Even some deep-sea species of hydromedusae and scyphomedusae are usually collected on or near the bottom. All of the stauromedusae are found attached to either seaweed or rocky or other firm material on the bottom.

 

Some species explicitly adapt to tidal flux. In Roscoe Bay, jellyfish ride the current at ebb tide until they hit a gravel bar, and then descend below the current. They remain in still waters until the tide rises, ascending and allowing it to sweep them back into the bay. They also actively avoid fresh water from mountain snowmelt, diving until they find enough salt.

  

Parasites

Jellyfish are hosts to a wide variety of parasitic organisms. They act as intermediate hosts of endoparasitic helminths, with the infection being transferred to the definitive host fish after predation. Some digenean trematodes, especially species in the family Lepocreadiidae, use jellyfish as their second intermediate hosts. Fish become infected by the trematodes when they feed on infected jellyfish.

 

Relation to humans

Jellyfish have long been eaten in some parts of the world. Fisheries have begun harvesting the American cannonball jellyfish, Stomolophus meleagris, along the southern Atlantic coast of the United States and in the Gulf of Mexico for export to Asia.

 

Jellyfish are also harvested for their collagen, which is being investigated for use in a variety of applications including the treatment of rheumatoid arthritis.

 

Aquaculture and fisheries of other species often suffer severe losses – and so losses of productivity – due to jellyfish.

 

Products

Main article: Jellyfish as food

In some countries, including China, Japan, and Korea, jellyfish are a delicacy. The jellyfish is dried to prevent spoiling. Only some 12 species of scyphozoan jellyfish belonging to the order Rhizostomeae are harvested for food, mostly in southeast Asia. Rhizostomes, especially Rhopilema esculentum in China (海蜇 hǎizhé, 'sea stingers') and Stomolophus meleagris (cannonball jellyfish) in the United States, are favored because of their larger and more rigid bodies and because their toxins are harmless to humans.

 

Traditional processing methods, carried out by a jellyfish master, involve a 20- to 40-day multi-phase procedure in which, after removing the gonads and mucous membranes, the umbrella and oral arms are treated with a mixture of table salt and alum, and compressed. Processing makes the jellyfish drier and more acidic, producing a crisp texture. Jellyfish prepared this way retain 7–10% of their original weight, and the processed product consists of approximately 94% water and 6% protein. Freshly processed jellyfish has a white, creamy color and turns yellow or brown during prolonged storage.

 

In China, processed jellyfish are desalted by soaking in water overnight and eaten cooked or raw. The dish is often served shredded with a dressing of oil, soy sauce, vinegar and sugar, or as a salad with vegetables. In Japan, cured jellyfish are rinsed, cut into strips and served with vinegar as an appetizer. Desalted, ready-to-eat products are also available.

 

Biotechnology

The hydromedusa Aequorea victoria was the source of green fluorescent protein, studied for its role in bioluminescence and later for use as a marker in genetic engineering.

Pliny the Elder reported in his Natural History that the slime of the jellyfish "Pulmo marinus" produced light when rubbed on a walking stick.

 

In 1961, Osamu Shimomura extracted green fluorescent protein (GFP) and another bioluminescent protein, called aequorin, from the large and abundant hydromedusa Aequorea victoria, while studying photoproteins that cause bioluminescence in this species. Three decades later, Douglas Prasher sequenced and cloned the gene for GFP. Martin Chalfie figured out how to use GFP as a fluorescent marker of genes inserted into other cells or organisms. Roger Tsien later chemically manipulated GFP to produce other fluorescent colors to use as markers. In 2008, Shimomura, Chalfie and Tsien won the Nobel Prize in Chemistry for their work with GFP. Man-made GFP became widely used as a fluorescent tag to show which cells or tissues express specific genes. The genetic engineering technique fuses the gene of interest to the GFP gene. The fused DNA is then put into a cell, to generate either a cell line or (via IVF techniques) an entire animal bearing the gene. In the cell or animal, the artificial gene turns on in the same tissues and the same time as the normal gene, making a fusion of the normal protein with GFP attached to the end, illuminating the animal or cell reveals what tissues express that protein—or at what stage of development. The fluorescence shows where the gene is expressed.

 

Aquarium display

Jellyfish are displayed in many public aquariums. Often the tank's background is blue and the animals are illuminated by side light, increasing the contrast between the animal and the background. In natural conditions, many jellies are so transparent that they are nearly invisible. Jellyfish are not adapted to closed spaces. They depend on currents to transport them from place to place. Professional exhibits as in the Monterey Bay Aquarium feature precise water flows, typically in circular tanks to avoid trapping specimens in corners. The outflow is spread out over a large surface area and the inflow enters as a sheet of water in front of the outflow, so the jellyfish do not get sucked into it. As of 2009, jellyfish were becoming popular in home aquariums, where they require similar equipment.

 

Stings

Jellyfish are armed with nematocysts, a type of specialized stinging cell. Contact with a jellyfish tentacle can trigger millions of nematocysts to pierce the skin and inject venom, but only some species' venom causes an adverse reaction in humans. In a study published in Communications Biology, researchers found a jellyfish species called Cassiopea xamachana which when triggered will release tiny balls of cells that swim around the jellyfish stinging everything in their path. Researchers described these as "self-propelling microscopic grenades" and named them cassiosomes.

 

The effects of stings range from mild discomfort to extreme pain and death. Most jellyfish stings are not deadly, but stings of some box jellyfish (Irukandji jellyfish), such as the sea wasp, can be deadly. Stings may cause anaphylaxis (a form of shock), which can be fatal. Jellyfish kill 20 to 40 people a year in the Philippines alone. In 2006 the Spanish Red Cross treated 19,000 stung swimmers along the Costa Brava.

 

Vinegar (3–10% aqueous acetic acid) may help with box jellyfish stings but not the stings of the Portuguese man o' war. Clearing the area of jelly and tentacles reduces nematocyst firing. Scraping the affected skin, such as with the edge of a credit card, may remove remaining nematocysts. Once the skin has been cleaned of nematocysts, hydrocortisone cream applied locally reduces pain and inflammation. Antihistamines may help to control itching. Immunobased antivenins are used for serious box jellyfish stings.

 

In Elba Island and Corsica dittrichia viscosa is now used by residents and tourists to heal stings from jellyfish, bees and wasps pressing fresh leaves on the skin with quick results.

 

Mechanical issues

Jellyfish in large quantities can fill and split fishing nets and crush captured fish. They can clog cooling equipment, having disabled power stations in several countries; jellyfish caused a cascading blackout in the Philippines in 1999, as well as damaging the Diablo Canyon Power Plant in California in 2008. They can also stop desalination plants and ships' engines.

S’il vous plaît note: 1 lote = 20 pcs Manfrotto + 20 pcs clip titulaire + 20 pcs Bluetooth d’obturation = 60 pcs/lote

Caractéristiques de manfrotto:

100% tout neuf et de haute qualité

Poids léger,...

 

telephone.pascherenchine.com/products/60-pcs-bluetooth-ca...

Prototype of the Mercury, an infinitely extensible, open camera system that I developed over the past two years, with some help from others. This one is shown configured to shoot Instax Mini. I've modified the Diana Instant Back with new parts so that it can mate with the camera. It uses the Graflok 23 (medium format) standard mount.

The spot-billed pelican or grey pelican (Pelecanus philippensis) shot at Vedanthangal. Check out its clear eyes and spots in the bill that has given the bird its name.

 

Also check out the extended frills below its bill, which gives it the extraordinary ability to use it as a fishing net and catch fish. They can hold up to 50 fish at a time before swallowing them up. These pelicans are also able to kill and eat anything that fits within this extensible pouch in their lower bill.

50 pcs DHLFree profissional rainures sur bâton Mobile téléphone caméra trépied extensible portrait de poche Manfrotto

 

Facile à prendre photo!

Note: ce téléphone...

 

telephone.pascherenchine.com/products/50-pcs-dhlfree-groo...

Paper Wasp using extensible "arm" to retrieve and eat.