1 Tectura virginea. Shell-length 6mm. From top down: anterior, posterior and lateral views. North Yorkshire. September 2014.

Shell a low conoid; ground colour whitish tinted pale-pink; threadlike radiating striae obscure/absent on this specimen.

 

Full SPECIES DESCRIPTION BELOW (Revised 2020)

Sets of OTHER SPECIES at: www.flickr.com/photos/56388191@N08/collections/

Revised, 2020, PDF version at www.researchgate.net/profile/Ian_Smith19/research

 

Tectura virginea (O.F. Müller, 1776)

 

Current taxonomy: World Register of Marine Species (WoRMS)

www.marinespecies.org/aphia.php?p=taxdetails&id=153552

Synonyms: Patella virginea O.F. Müller, 1776, 1776; Patelloida virginea (O.F. Müller, 1776); Acmaea virginea (O.F. Müller, 1776); Acmaea virginica in Yonge & Thompson, 1976;

Vernacular names: White tortoiseshell limpet; Pink-rayed limpet (English); Brenigen wen (Welsh); Stribet albueskael (Danish); schoteltje (Dutch); Jungfräuliche Napfschnecke (German); jomfrusnegl (Norwegian); jungfruskålsnäcka (Swedish);

 

GLOSSARY below.

 

Shell Description

Up to 12 mm long. Often thin and fragile. Usually a low conoid 1Tv flic.kr/p/tg3YWR , occasionally high. Excentric apex tilted forwards, usually 18% to 30% of shell-length from anterior; sometimes more central on sublittoral specimens. Base oval, sometimes widest at posterior 2Tv flic.kr/p/sYsjKh . Anterior profile slightly concave; posterior profile slightly convex; often distinct changes in slope 3Tv flic.kr/p/tg3WuB . Sculpture of slight threadlike radiating striae 2Tv flic.kr/p/sYsjKh , often indistinct or absent 1Tv flic.kr/p/tg3YWR , and numerous fine concentric growth lines, sometimes emphasised by algal growths 4Tv flic.kr/p/sYAote ; smooth surface unless coated with Lithothamnion 5Tv flic.kr/p/sj3eSy Young shells are translucent with a tiny, white, semi-spiral, apical protoconch 40Tv flic.kr/p/2jQTrLN discernible until the shell is about 1.5mm long, after which it is usually eroded. External ground colour of live shell whitish, often tinted pale-pink 1Tv flic.kr/p/tg3YWR or pale-blue 3Tv flic.kr/p/tg3WuB . Central early growth usually patterned with tessellating chains of light brown, sometimes with bright blue spot in each link 3Tv flic.kr/p/tg3WuB ; frequently worn off older shells 2Tv flic.kr/p/sYsjKh . On later peripheral growth 16-20 flaring, radiating, pink to liver-coloured rays usually replace chains 6Tv flic.kr/p/sj3bKb . Colours fade rapidly after death 2Tv flic.kr/p/sYsjKh . Internally, shell often translucent whitish, with some exterior markings showing through 7Tv flic.kr/p/tg6zWx ; sometimes red-brown, complete or partial V with point near vertex and arms to posterior 2Tv flic.kr/p/sYsjKh .

Older shells often lined with thin porcellaneous layer that reduces translucency and conceals exterior markings. In fresh shells, often distinct U-shape shell-muscle scar, broad peripheral whitish pallial band, and central white viscera patch 8Tv flic.kr/p/sjeoa3 . Fragile shells soon beach-worn and faded after death; older shells and those reinforced by coating of Lithothamnion (opaque chalky white when dead) survive best and most frequently found on strand-line 9Tv flic.kr/p/tghKfR .

 

Body description

Main colour of flesh white, yellowish or pinkish. Head has short stout snout with large mouth. When not feeding, outer lip forms large prominent ridge with loose lateral flaps around anterior and sides of mouth10Tv flic.kr/p/sjq6gF . When feeding, outer lip expands into translucent oral veil on substrate 11Tv flic.kr/p/tfYATC & 12Tv flic.kr/p/tdUW2w . Long, slender, unpigmented cephalic tentacles, wrinkled when not fully extended 11Tv flic.kr/p/tfYATC . Black eye on dorsum of base of each tentacle, but difficult to view when live as not extended beyond shell and, when viewed ventrally, usually obscured by tentacle 13Tv flic.kr/p/tfYzmE ; also eye often unpigmented so obscure. Red buccal mass shows pink through parts of head 14Tv flic.kr/p/tdUUSs . Mantle-skirt white 12Tv flic.kr/p/tdUW2w , yellowish 13Tv flic.kr/p/tfYzmE , or blue-green 14Tv flic.kr/p/tdUUSs with reddish bands on periphery that produce corresponding rays of shell 14Tv flic.kr/p/tdUUSs . Mantle cavity consists of nuchal cavity over head, and groove (lacking pallial gills) around periphery of foot 14Tv flic.kr/p/tdUUSs . Substantial single ctenidium with short lamellae, colour similar to mantle, attached inside left of nuchal cavity and extends across to right 15Tv flic.kr/p/sYFKbL . Unlike in most gastropods, ctenidium not attached to cavity roof or floor, other than at its base, and lamellae lack internal skeleton, so able to contract to 50% of size and withdraw completely into nuchal cavity above head 14Tv flic.kr/p/tdUUSs ; but tip sometimes visible over right “shoulder” 13Tv flic.kr/p/tfYzmE . When animal moving, ctenidium often fully extended but hidden between shell and extended foot/outer lip 12Tv flic.kr/p/tdUW2w , except occasionally tip protrudes beyond shell. Clear view of ctenidium possible when inverted animal stretches to right itself 16Tv flic.kr/p/sYH1Lo . Periphery of mantle has many large white 'repugnatorial glands' set back from mantle edge and connected to it by narrow white necks 14Tv flic.kr/p/tdUUSs . Outer edge of mantle has many small, unobtrusive, translucent, cilia-bearing sensory processes 17Tv flic.kr/p/sYPNR6 . U of white muscle bundles 13Tv flic.kr/p/tfYzmE (blood vessels pass through the gaps), may be tinted as mantle , attaches body/foot to shell 18Tv flic.kr/p/tg1VSW . Foot yellow 13Tv flic.kr/p/tfYzmE or white 11Tv flic.kr/p/tfYATC ; sole oval, sometimes shows viscera 19Tv flic.kr/p/sjgCkU . When crawling, usually only long whitish cephalic tentacles 6Tv flic.kr/p/sj3bKb , and occasionally tip of ctenidium, visible dorsally; and whitish sides of foot and head visible laterally 11Tv flic.kr/p/tfYATC ; no epipodial tentacles on side of foot. No penis as fertilization external.

 

Internal anatomy visible with simple dissection

When shell is removed, whole mantle is exposed; part within U-shape shell-muscle is translucent so several features can be seen through it 20Tv flic.kr/p/sYGWq9 , but are more easily viewed if it is removed.

Key to images: 20Tv flic.kr/p/sYGWq9 , 21Tv flic.kr/p/sYFDp5 , 22Tv flic.kr/p/tdYS1N , 23Tv flic.kr/p/sjie7f , 24Tv flic.kr/p/tdYR6G , 25Tv flic.kr/p/tg3tWy , 26Tv flic.kr/p/sYHf5L ,

 

1: black or purple-black eye at base of cephalic tentacle. (images 21-24Tv)

2: yellow-buff odontophore supporting distal section of radula (image 24Tv)

3: buccal mass in translucent head (image 20-23Tv)

4: radula (images 23-26Tv)

5: radula sac enclosing proximal section of radula (24 & 26Tv)

6: yellow of radula visible through translucent head (images 22-23Tv)

7: roof of nuchal cavity (image 20Tv)

8: ctenidium, greatly contracted after death. (image 22Tv)

9: greyish stomach wall (images 20-21Tv)

10: digestive gland (images 20-21Tv)

11: rectum containing pale faecal pellets (image 23Tv)

12: yellow-buff male gonad (images 20-21Tv)

13: remains of ruptured female ovary (image 22Tv)

14: ova scattered from ovary (image 22Tv)

15: severed U shape shell-muscle (images 20-24Tv)

16: mantle skirt (images 20-22Tv & 24Tv)

17: muscles of left side of sole (image 24Tv)

18: jaw (image 26Tv)

cartilage of odontophore (image 25Tv)

 

Key identification features

Young Patella spp., can resemble worn specimens of T. testudinalis.

 

Tectura virginea

1) Maximum length 12 mm.

2) Shell exterior whitish/yellowish/bluish with pinkish or brownish rays and chains 11Tv flic.kr/p/tfYATC Worn specimens of T. virginea are often mistaken for T. testudinalis; examination of the foot and pallial groove or shell interior is necessary in such cases 34Tv flic.kr/p/2jcJrNh . Young T. virginea with blue spots 3Tv flic.kr/p/tg3WuB often confused with early stage Patella pellucida 36Tv flic.kr/p/2jcEoK7 .

3) Shell interior white, often shows exterior marks, sometimes red-brown V at vertex 2Tv flic.kr/p/sYsjKh .

4) Threadlike radial striae and fine concentric growth lines 2Tv flic.kr/p/sYsjKh often indistinct 1Tv flic.kr/p/tg3YWR

5) Mantle-skirt white, yellowish, or blue-green with inwardly oriented, large, white glands, and reddish bands on periphery 12 Tv flic.kr/p/tdUW2w 13 Tv flic.kr/p/tfYzmE & 14 Tv flic.kr/p/tdUUSs . Ctenidium, no pallial gills 16 Tv flic.kr/p/sYH1Lo .

6) Many unobtrusive, translucent processes on mantle edge, but no pallial tentacles 17 Tv flic.kr/p/sYPNR6 .

7) All Britain except NE Irish Sea and parts of SE England. On encrusted rock, not seaweeds.

8) Apex 18% to 30% of length from anterior 2 Tv flic.kr/p/sYsjKh .

 

Similar species

Testudinalia testudinalis (O. F. Müller, 1776)

1) Maximum length usually 20 mm, occasionally 25 mm 31Tv flic.kr/p/2jcH6iR .

2) Shell exterior matt-whitish with radiating dark brown rays that often bifurcate and reunite across the shell 30Tv flic.kr/p/2jcH6nd .

3) Shell interior porcelaneous-white with brown-banded peripheral border, and dark brown viscera patch, usually with pale vertex patch 33Tv flic.kr/p/2jcH6eh .

4) Fine concentric growth lines and radiating striae 32Tv flic.kr/p/2jcEoS6 .

5) Mantle skirt green in pallial groove, no red bands or large white glands on mantle periphery. Ctenidium, no pallial gills 34Tv flic.kr/p/2jcJrNh .

6) Large pallial tentacles protrude beyond shell perimeter when active 34Tv flic.kr/p/2jcJrNh .

7) North U.K, to Anglesey and N. Yorkshire. Many absence records, misleadingly, mapped further south on NBN with same symbol as for presence. On encrusted rock, not on seaweeds. records.nbnatlas.org/occurrences/search?q=lsid:NHMSYS0021...

8) Apex c. 25% to 40% of length from anterior 32Tv flic.kr/p/2jcEoS6 .

 

Patella pellucida Linnaeus, 1758 [early stage, length 2 to 7mm]

1) Maximum length of development stage 7 mm.

2) Shell exterior translucent pale horn to light brown with blue/green hyphens in longitudinal rows 36Tv flic.kr/p/2jcEoK7 . not in links of a chain pattern like that on some young T. virginea 3Tv flic.kr/p/tg3WuB .

3) Shell interior pale horn to light brown with black, colloidal particles under parts of the blue/green hyphens.

4) Smooth fragile shell 36Tv flic.kr/p/2jcEoK7 .

5) Mantle-skirt translucent whitish. Pallial gills, no ctenidium in nuchal cavity. No inwardly oriented, large, white repugnatorial glands or reddish bands on mantle periphery 35Tv flic.kr/p/2jcEoKC

6) pallial tentacles protrude from aperture rim, but unobtrusive as translucent and almost invisible 35Tv flic.kr/p/2jcEoKC .

7) All round Britain except Liverpool Bay and parts of SE England. On Laminaria, not rock, when > 2mm long.

8) Apex lost from anterior rim of aperture 36Tv flic.kr/p/2jcEoK7 .

 

 

Williamia gussoni (Costa O. G., 1829) 37Tv flic.kr/p/2jcJrJQ

1) Usual shell length c. 6 mm. Maximum L. c. 8 mm, W. 6 mm and H. 3 mm (Ruthensteiner, 2006); L. 8.8 mm (P. Ugarković, 2020 pers. comm.)

2) Exterior of shell is shiny, bright red-brown with c. 18 pale radiating rays that are sometimes obscured or faded when dead. Periostracum extends well beyond rim of shell.

3) Shell interior as exterior, but paler.

4) Thin, smooth shell with convex anterior and posterior slopes.

5) Mantle is translucent, red-brown with radiating, opaque white rays which correlate with pale rays of shell. No inwardly oriented, large, white repugnatorial glands. In Siphonariidae; respires with c. 17 lamellae concealed in mantle cavity; no pallial gills or protruding ctenidium plume.

6) No pallial tentacles. Cephalic tentacular lobes separated from large flat head by small cleft. Large flap-like anal lobe protrudes from mantle cavity on right. Dorsal surface of head and foot are red-brown; ventrally yellowish white

7) Common at Low Water to more than 50 m (J. Prkić, 2020, pers. comm.) in Adriatic, Mediterranean and adjacent Atlantic; not N.W. Europe (Ruthensteiner, 2006).

8) Apex has distinct semi-spiral protoconch positioned off-centre posteriorly, sometimes overhanging beyond the posterior of the aperture.

Habits and ecology

On rocky shores where turbidity doesn't prevent plant growth; at LWST (higher level if in pools) and to 100m depth. Occurs and feeds on pink Lithothamnion algae encrusting bedrock and stable stones 27Tv flic.kr/p/tdYPYw . Diatoms, Chondrus crispus and Cystoseira also reported as food (Fretter & Graham, 1962). So long as not arid, tops of encrusted stones and rocks apparently preferred, perhaps to avoid silt, but also where light allows Lithothamnion to grow. Hard iron-mineralized radula, longer than shell to allow for replacement of teeth worn away on rock, aided by pair of grab-like, lateral, chitinized jaws, 26Tv flic.kr/p/sYHf5L produces a distinctive network of feeding pits in surface of Lithothamnion 28Tv flic.kr/p/tgiReX ; initially paler-pink than undamaged surface but later bleaching white as Lithothamnion is killed 27Tv flic.kr/p/tdYPYw . Wide outer lip spreads out flat on substrate during feeding 11Tv flic.kr/p/tfYATC , contains many sensory structures; possible functions to detect Lithothamnion, locate mouth precisely to avoid overlap with previous feeding pit without missing part of food, and to retain loose fragments (function of anterior scraper-jaw on Patella spp.; missing from T. virginea). Long coiled intestine compacts faeces into firm white pellets 23Tv flic.kr/p/sjie7f that will not contaminate ctenidium near anus in nuchal cavity (T. virginea lacks a hypobranchial gland to produce mucus to bind faecal fragments). After defecation, pellets carried by exhalent respiratory current to posterior of animal to accumulate under shell 28Tv flic.kr/p/tgiReX before periodic sharp contraction of shell-muscle clamps shell down to expel water and faeces.

Defence: when on Lithothamnion, colour cryptic, and chain pattern 3Tv flic.kr/p/tg3WuB resembles feeding pits 28Tv flic.kr/p/tgiReX ; also shell often has covering of Lithothamnion 5Tv flic.kr/p/sj3eSy . Cilia-bearing sensory processes on outer edge of mantle 17Tv flic.kr/p/sYPNR6 probably sense attack. In response to strong stimulation (e.g. pressure from forceps) white repugnatorial glands on mantle-fringe 14Tv flic.kr/p/tdUUSs emit secretion of viscid, slow-to disperse, white threads (presumed by Fretter & Graham, 1962, to be distasteful and/or toxic) 29Tv flic.kr/p/t6rdC9 .

Breeds in spring (April-May in Roscoff); shedding of sperm into water by males (probably proximate, perhaps on female's shell like Testudinalia testudinalis) stimulates females to release eggs individually 22Tv flic.kr/p/tdYS1N . Eggs hatch as free trochophore larvae (stage passed within egg by most less “primitive” spp.) in plankton before transforming to veligers and, after a short pelagic life, settling and assuming limpet form with the white, semi-spiral, veliger shell at the apex as a protoconch 40Tv flic.kr/p/2jQTrLN . The protoconch is usually eroded away after the shell is about 1.5 mm long.

Respiration: cilia on ctenidium create inhalent water current into left of nuchal cavity, then between ctenidial filaments to oxygenate blood within, and thence as exhalent current along pallial groove on each side of foot to exit at posterior of limpet 18Tv flic.kr/p/tg1VSW . Although no pallial gills, respiration probably also occurs in pallial groove as most blood from head and pedal veins passes in veins through gaps between shell-muscle bundles into mantle and collects in peripheral efferent pallial vessel 18Tv flic.kr/p/tg1VSW (Fretter & Graham, 1962) that probably acquires oxygen from current generated by ctenidium and/or external water at shell's edge. Blood passes from efferent pallial vessel to heart without going through ctenidium 10Tv flic.kr/p/sjq6gF . When emersed, mantle cavity drains and ctenidium collapses, but roof of richly-vascularized cavity stays damp and functions for gas exchange sufficiently for respiration for short periods.

 

Distribution and status

Iceland and Kola Peninsula (N. Russia) to Senegal and into Mediterranean, not Baltic. GBIF map www.gbif.org/species/5191383 No record has been found of it living intertidally in the Mediterranean (J. Prkić, Croatia and G. Bazios, Greece, 2020, pers. comm.). Frequent all round Britain and Ireland on hard substrate in non-turbid water. Frequent all round Britain and Ireland on hard substrate in non-turbid water. It is absent, or rare, in Liverpool Bay and further south than Flamborough Head to Kent. U.K. map NBN species.nbnatlas.org/species/NHMSYS0021056385

 

Acknowledgements

I should like to thank Dr Ivan Nekhaev and Dr Julia Sigwart, for advice with the text and interpretation of the images. I thank Jakov Prkić and Pero Ugarković for information and use of images, Simon Taylor and Andrew Wright for specimens and Ann Wake and Allan Rowat for use of images. Any errors or omissions are the responsibility of the author.

 

Links and references

Forbes, E. & Hanley S. 1849-53. A history of the British mollusca and their shells. vol. 2 (1849), London, van Voorst. (As Acmaea virginea; Free PDF at archive.org/stream/historyofbritish02forb#page/436/mode/2up Use slide at base of page to select pp.437-440.)

 

Fretter, V. and Graham, A. 1962. British prosobranch molluscs. London, Ray Society.

Graham, A. 1988. Prosobranch and pyramidellid gastropods. London.

 

Jeffreys, J.G. 1862-69. British conchology. vol. 3 (1865). London, van Voorst. (As Tectura virginea; Free PDF at archive.org/stream/britishconcholog03jeff#page/248/mode/2up . Use slide at base of page to select pp.248- 250.

 

Yonge, C.M. and Thompson, T.E. 1976. Living marine molluscs. London.

Current taxonomy: World Register of Marine Species (WoRMS)

www.marinespecies.org/aphia.php?p=taxdetails&id=153552

 

GLOSSARY

 

aperture =– mouth of gastropod shell; outlet for head and foot.

cephalic =– (adj.) of or on the head.

ctenidium = comb-like molluscan gill; usually an axis with a row of filaments either side.

 

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

 

epipodial (adj.) = of the epipodium (collar or circlet running round sides of foot of some gastropods).

 

mantle = sheet of tissue that secretes the shell and forms a cavity for the gill in most marine molluscs.

 

MLWS = mean low water spring tide level (mean level reached by lowest low tides for a few days every fortnight; Laminaria or Coralline zone on rocky coasts).

 

periostracum = thin horny layer of chitinous material often coating shells.

 

trochophore = spherical or pear-shaped larva that swims with aid of girdle of cilia. Stage preceding veliger, passed within gastropod egg in most spp. but free in plankton for patellid limpets, most Trochidae and Tricolia pullus.

 

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

 

Done