02 Acanthodoris pilosa

High dome profile. Mantle covers whole body, except posterior of foot protrudes beyond mantle when in motion (1).

Length 11 mm, Menai Strait, Wales. March 2015.

 

Full SPECIES DESCRIPTION BELOW

Sets of OTHER SPECIES:

www.flickr.com/photos/56388191@N08/collections/

 

Acanthodoris pilosa (Abildgaard in Müller, 1789)

Current taxonomy: World Register of Marine Species (WoRMS) www.marinespecies.org/aphia.php?p=taxdetails&id=140627

 

Synonyms: Doris pilosa Abildgaard in Müller, 1789 ; Doris subquadrata Alder & Hancock, 1845; Acanthodoris subquadrata (Alder & Hancock, 1845);

Meaning of name:

Acanthodoris = (Greek akantha )Thorny + Doris (name of a sea nymph).

pilosa (Latin) = pilose / hairy / furry / shaggy

 

GLOSSARY below.

 

Body

Up to 40mm long, exceptionally 55mm; high dome profile. Mantle covers whole body; varies white 1Ap flic.kr/p/MVByj4 , brown 2Ap flic.kr/p/NTLFkr , black,or yellow (P.Lightfoot) flic.kr/p/oJLWhQ . Pale colours may be mottled or freckled darker, especially on juveniles 3Ap flic.kr/p/NrccVy . Translucent pale forms usually reveal pale brown/ yellowish orange viscera 4Ap flic.kr/p/NKYeKt . Long, fine, radially arranged spicules often visible in mantle when viewed from below 5Ap flic.kr/p/NQxsVm ; do not interlock, so body soft and yielding. Soft, tall, thin, conical tubercles on mantle 6Ap flic.kr/p/Nrc9wu give shaggy/ pilose appearance 4Ap flic.kr/p/NKYeKt , but sometimes can be somewhat contracted and less distinctive (J.Anderson) flic.kr/p/Aes3Cj . Alder & Hancock mistakenly based a separate species, Doris subquadrata 1845, on a single specimen with small conical tubercles www.biodiversitylibrary.org/item/131598#page/158/mode/1up

Rhinophores

Long, rising from low sheath with tuberculated rim; base smooth, upper lamellated part often bent backwards 7Ap flic.kr/p/NQxst9 . Approximate number of lamellae on one rhinophore at different body lengths: 10 at 4.4mm, 13 at 6mm, 18 at 11mm, 21 at 17mm, 24 at 30mm; numbers include apical 'nipple' which is lamellae held upwards. Left and right lamellae meet at anterior groove and as posterior 'V' 8Ap flic.kr/p/NKYcGF . Translucent, usually coloured as mantle, lamellae of white specimens often slightly cream yellow 4Ap flic.kr/p/NKYeKt , occasionally bright orange (K.G.Pedersen) flic.kr/p/bSuKzV . Rhinophores often held obliquely sideways 9Ap flic.kr/p/MVXQ3u .

Gills

Up to nine voluminous tripinnate gills in circle around anus 4Ap flic.kr/p/NKYeKt ,10Ap flic.kr/p/NHsoPU & 11Ap flic.kr/p/NQxpeU . Usually translucent and tinted as mantle, with some opaque white along each side of midrib forming a star; sometimes opaque white on lamellae. When disturbed, gills contract separately down to mantle surface 3Ap flic.kr/p/NrccVy ; do not retract in unison into a pocket.

Head

Narrow oral veil extended laterally into broad, flat oral tentacles[4]. Anterior of veil has two protrusions centrally 12Ap flic.kr/p/Nrc6WE .

Foot

Sole translucent white, showing opaque whitish gonads 13Ap flic.kr/p/NHsntC or pale brown 5Ap flic.kr/p/NQxsVm or brownish orange 15Ap flic.kr/p/NQxkbJ viscera centrally . Sometimes a few dark pigment marks on sole 12Ap flic.kr/p/Nrc6WE . Dorsal surface of foot similar to mantle; whitish 14Ap flic.kr/p/MVXK65 freckled sparsely 15Ap flic.kr/p/NQxkbJ or freckled densely 16Ap flic.kr/p/NHsmfq . Anterior and posterior of foot smoothly rounded 13Ap flic.kr/p/NHsntC ; posterior protrudes beyond mantle when in motion 1Ap flic.kr/p/MVByj4 & 17Ap flic.kr/p/NHskGb . Locomotion by monotaxic retrograde waves on sole.

 

Key identification features

Acanthodoris pilosa

1: Soft, tall, thin, conical tubercles on mantle 6Ap flic.kr/p/Nrc9wu , but sometimes contracted/ poorly developed and not so distinctive (J.Anderson) flic.kr/p/Aes3Cj.

2: Body soft and yielding. Usual maximum length 40mm.

3: Voluminous tripinnate gills can contract but not retract into pocket; usually, opaque white along each side of midribs forms a star when gills expanded 4Ap flic.kr/p/NKYeKt .

4: Narrow oral veil extended laterally into broad, flat oral tentacles. Anterior of veil has two protrusions centrally. 12Ap flic.kr/p/Nrc6WE

5: Upper lamellated part of large rhinophores often bent backwards 7Ap flic.kr/p/NQxst9 .

 

Similar species

No other British dorid species has long soft conical tubercles, such large, often bent, rhinophores or its distinctive oral veil/flat oral tentacles, but specimens with contracted or poorly developed tubercles sometimes confused with other white or brownish dorids such as

Onchidoris muricata (O.F.Müller, 1776) :

1: Tubercles shaped as club with flat/slightly rounded tip 19Ap flic.kr/p/MVBhG2 .

2: Body quite firm with many spicules. Usual maximum length 14mm.

3: Simply pinnate small gills can retract into a pocket.

4: Broad rounded oral veil 20Ap flic.kr/p/NTLsRP .

 

Onchidoris proxima (Alder & Hancock, 1854)

1: Tubercles, torpedo shaped club with rounded point 21Ap flic.kr/p/MVBgbX .

2: Body quite firm with many spicules. Usual maximum length 17mm.

3: Simply pinnate small gills can retract into a pocket.

4: Broad rounded oral veil 21Ap flic.kr/p/MVBgbX .

 

Jorunna tomentosa (Cuvier, 1804)

1: Fine spiculose tubercles on mantle, "caryophyllidia" 22Ap flic.kr/p/NTLspB , under microscope somewhat resembling a clove (spice) in structure.

2: Body spiculate, fairly firm. Usual maximum length 60mm.

3. Expanded gills on raised collar 22Ap flic.kr/p/NTLspB around brown anus 23Ap flic.kr/p/MVBdgP . Gills can retract into pocket.

4: Head has small tentacles and no veil 22Ap flic.kr/p/NTLspB .

 

Cadlina laevis (Linnaeus, 1767)

1: Unobtrusive, very small, soft tubercles on mantle (J.Anderson) flic.kr/p/6e53ZS

2: Body has soft texture, a flattened low profile, is shiny white with opaque yellow or white marks near the periphery and, sometimes, has an opaque yellow or white peripheral border. Usual maximum length 32mm.

3: Gills not voluminous, hidden much of the time retracted into pocket.(J.Anderson) flic.kr/p/6e53ZS

4: Head has very small tentacles and no veil.

 

Habits and ecology

On mid- and lower-shore and sublittorally to about 170m.

Feeds on Alcyonidium hirsutum www.habitas.org.uk/marinelife/species.asp?item=Y1390 on shore, Alcyonidium diaphanum www.habitas.org.uk/marinelife/species.asp?item=Y1370 sublittorally, and occasionally on Flustrellidra hispida www.unterwasser-welt-ostsee.de/html/rotdorniges_moostierc... . Breeds when 8mm long and larger. Simultaneous hermaphrodite. Spawn (J.Anderson) flic.kr/p/Aes3Cj a convoluted ribbon attached by its edge, deposited in spiral of about two turns. Spawning in all months with maximum in spring (when adults commonest 18Ap flic.kr/p/MVXHi7 ) and secondary peak in autumn. Planktonic veliger larvae for about ten days at 10ºC before metamorphosis.

 

Distribution and status

Iceland to Morocco and western Baltic. Greenland to Virginea, and Alaska to Vancouver. Not within Arctic circle, rare in Mediterranean. GBIF map www.gbif.org/species/2292107 Common and widespread round Britain and Ireland. NBN UK map species.nbnatlas.org/species/NHMSYS0021056240

 

Acknowledgements

I would like to acknowledge and thank Paula Lightfoot, Jim Anderson and Kjetil Pedersen whose greatly valued images have been linked to this account. Jim's exceptionally good website and Flickr Albums can be seen at

www.nudibranch.org/Scottish%20Nudibranchs/

and www.flickr.com/photos/jim-anderson/albums

 

Links and references

Alder, J. & Hancock, A. 1845-1855. A monograph of the British nudibranchiate mollusca. London, Ray Society. www.biodiversitylibrary.org/item/131598#page/152/mode/1up &

www.biodiversitylibrary.org/item/131598#page/158/mode/1up

 

Catteneo Vietti, R., Angelini, S., Gaggero, L. & Lucchetti, G. 1995. Mineral composition of nudibranch spicules. J. Mollus. Stud. 61 (3): 331-337. Abstract at mollus.oxfordjournals.org/content/61/3/331.abstract

 

Picton, B.E. & Morrow, C.C. Encyclopedia of marine life of Britain and Ireland. [For prey]. www.habitas.org.uk/marinelife/index.html

 

Thompson, T.E. & Brown, G.H. 1984. Biology of opisthobranch molluscs 2. London, Ray Society.

 

Current taxonomy: World Register of Marine Species (WoRMS) www.marinespecies.org/aphia.php?p=taxdetails&id=140627

 

Glossary

cephalic (adj.) = of or on the head.

ELWS = extreme low water spring tide (usually near March and September equinoxes).

lamellae (sing. lamella) = small plates on rhinophores, or leaflets of gill.

mantle (of nudibranchs) = sheet of tissue forming part or all of notum (dorsal body surface).

 

monotaxic (of locomotion waves on foot) = single series of waves across complete width of foot.

 

myoglobin = red oxygen-binding protein in muscle tissue; often in buccal-mass muscles of gastropods. Similar to red haemoglobin in vertebrate blood, but green haemocyanin is usual oxygen-carrier in mollusc blood. See www.researchgate.net/publication/251227038_Radular_myoglo...

 

papilla = (pl. papillae) small cone-shaped protrusion of flesh.

papillate = covered in papillae.

plankton = animals and plants that drift in pelagic zone (main body of water).

retrograde (of locomotion waves on foot) = waves travel from anterior to posterior.

 

rhinophores (pl.) = chemo-receptor tentacles on top of head of nudibranch.

tripinnate (of gill plume) = threefold branching; “boughs, branches, twigs” in one plane like a feather.

 

spicule (in dorid seaslugs) = small, slender, sharp-pointed feature mainly composed of calcite (CaCO3) and brucite (Mg(OH)2) .

 

spiculate = containing spicules.

veliger = shelled larva of marine gastropod or bivalve mollusc which swims by beating cilia of a velum (bilobed flap).

Done