01 Patella depressa. Length 32mm, height 9.1mm. S. Devon. September 1997. Leg. J. Light.

Near maximum length (c.35mm) for the species.

1: posterior profile slightly convex.

2: anterior profile straight.

3: excavated vertex patch.

 

SPECIES DESCRIPTION part A BELOW

SPECIES DESCRIPTION part B 2Pd flic.kr/p/AfbFkR

Key id. features 3Pd flic.kr/p/Ay7bhf

PDF version at www.researchgate.net/profile/Ian_Smith19/research

 

OTHER SPECIES ALBUMS www.flickr.com/photos/56388191@N08/collections/

 

Patella_depressa Pennant, 1777

 

Current taxonomy: World Register of Marine Species (WoRMS)

www.marinespecies.org/aphia.php?p=taxdetails&id=151374

Synonyms: Patella intermedia Murray in Knapp,1857; Patella vulgata var. intermedia Jeffreys, 1865; Patella athletica [as dark variant of] Forbes & Hanley,1849;

Jeffreys (1865) mistakenly took the rudimentary description of P. depressa by Pennant (1777) to be what is currently (2015) called P. ulyssiponensis Gmelin, 1791 (syn. P. athletica). Until 1923, most authors followed Jeffreys in applying the name P. depressa Pennant to the wrong species, and in using the name P. intermedia Jeffreys for what is now recognised as P. depressa Pennant. Examination of Pennant's type specimen by Tomlin (1923) exposed the error and authors started to use the name P. athletica Bean, 1844, for what is now called P. ulyssiponensis but, probably to avoid confusion, many retained use of P. intermedia Jeffreys for the true P. depressa Pennant, despite Pennant's priority, until the 1970s (e.g.Yonge & Thompson, 1976).

Vernacular names: Black footed limpet (English); Brenigen dorddu (Welsh); Platte schaalhoren (Dutch); Patelle bernique (French);

 

Meaning of name:

Patella (Latin) = little pan. depressa (Latin) = depressed /low.

 

Terms in text used with restricted or specialised meaning are marked with hashtag#; refer to GLOSSARY below.

 

Shell Description

Patellid limpets have great geographical variation within and between species. This account refers to typical British specimens.

Usual maximum length c.35mm and height# 12mm 1Pd flic.kr/p/BaSA3C . Strong. Conoid; apex is positioned to anterior of centre. The base is ovoid , widest and sometimes angulated at posterior. Profile usually low (H/L 25-37% in sample of twelve typical shells from S.W.England and N.W. Wales) 2Pd flic.kr/p/AfbFkR . In profile, anterior and posterior usually slightly convex or almost straight. Sculpture of narrow, radiating, whitish ribs that tend to be arranged in triplets; one major flanked by a minor each side 10Pd flic.kr/p/BaScwq . Ribs project as points from aperture-rim of unworn shells 3Pd flic.kr/p/Ay7bhf , but often majority have ribs rounded, and rib-points reduced, by erosion, and outer shell-layer eroded away from apical half of the shell 4Pd flic.kr/p/Bc5Hk6 to almost whole shell 5Pd flic.kr/p/Ay7kFz . Dark radiating rays in grooves of exterior shell-layer visible externally only on uneroded parts 4Pd flic.kr/p/Bc5Hk6 , but usually clearly visible on interior through transparent, iridescent skirt-shell-layer# for much 6Pd flic.kr/p/Ay7i76 or most 7Pd flic.kr/p/AfbuN8 of the way to opaque, whitish, pallial-groove-band#. On interior, whitish projecting points of ribs have short, unglazed, chalky-white central line, but reduced or lacking where projecting point of rib eroded 8Pd flic.kr/p/Ay6YL9 . Pedal-retractor muscle leaves translucent horseshoe-shape scar 7Pd flic.kr/p/AfbuN8 , often containing an opaque white line 9Pd flic.kr/p/Ay7bJg . Mouth of horseshoe-scar is closed by thin anterior mantle-attachment scar 9Pd flic.kr/p/Ay7bJg ; the two scars enclose area shaped like fat amphora# filled with blackish 10Pd flic.kr/p/BaScwq , grey 11Pd flic.kr/p/Bd4YEr , orange-cream 12Pd flic.kr/p/Af3iJS , opaque-white and/or yellowish-cream 7Pd flic.kr/p/AfbuN8 shell-layer. Some have excavated, colourless, translucent patch near vertex#, 13Pd flic.kr/p/AApFbT , perhaps caused by re-absorption of shell-material. Juvenile spat lack ridges on main antero-posterior axis and have broad, prominent, mid-lateral pigment lines from apex to lip that are swept forwards on left and backwards on right.

 

Body description

Translucent white head, darkened to purple-pink by internal odontophore 14Pd flic.kr/p/Bc5hcv ; has substantial snout , slit at posterior, with large mouth (transverse when shut) fringed by thick outer lips 15Pd flic.kr/p/Ay6H2J . Distal end of snout and lips tinted pale yellow 14Pd flic.kr/p/Bc5hcv . When outer lips opened, dull-yellow inner lips exposed. Inner lips open laterally to expose radula with crimson ribbon and golden teeth, and white, cuticularized, triangular licker 15Pd flic.kr/p/Ay6H2J . Sturdy pale grey cephalic tentacles have small black eye in slight swelling at base 2Pd flic.kr/p/AfbFkR . Eye is primitive (or degenerate) cavity, open to seawater and lined with black retina cells. Mantle-skirt translucent buff 16Pd flic.kr/p/Afb9yv ; colour most saturated and translucency least when skirt retracted from shell-periphery 17Pd flic.kr/p/BaRWfU . Mantle cavity consists of nuchal cavity over head, and pallial groove filled with pallial gills around entire periphery of foot-head 16Pd flic.kr/p/Afb9yv ; no ctenidium. Each gill is tongue-shaped leaflet attached by stalk to distal wall of pallial-groove, and has densely ciliated groove on stalk and thickened rim 18Pd flic.kr/p/Bc59v8 . Efferent pallial vessel in mantle-skirt, close to pallial-groove, enters nuchal cavity on left 16Pd flic.kr/p/Afb9yv . Mantle-edge has many opaquely-pigmented chalky-white pallial tentacles, becoming translucent and less intensely coloured only in a small distal portion; tentacles distinct from translucent, buff mantle-skirt that they arise from 19Pd flic.kr/p/Af37zY . Around perimeter, pallial tentacles alternate single long with several short. Length of pallial tentacles, and their position relative to shell, vary with degree of extension of mantle skirt 20Pd flic.kr/p/Ay6PEH , 21Pd flic.kr/p/Azyo2Q and 17Pd flic.kr/p/BaRWfU . Pedal-retractor muscle arranged in horseshoe pattern of white muscle bundles demarcated by gaps 20Pd flic.kr/p/Ay6PEH ; muscle attaches body/foot to shell (a.k.a. shell muscle) 17Pd flic.kr/p/BaRWfU . Sole of foot approximately circular 20Pd flic.kr/p/Ay6PEH to oval with slightly tapered posterior 21Pd flic.kr/p/Azyo2Q , pitch-brown to black with pale peripheral rim, colour most saturated when foot contracted 17Pd flic.kr/p/BaRWfU . White sides of foot lack features such as epipodial tentacles 2Pd flic.kr/p/AfbFkR . When crawling, usually only extended pallial tentacles and, perhaps, tips of cephalic tentacles protrude beyond shelter of shell 22Pd flic.kr/p/BexkLe . No penis as fertilization external.

 

Further detail visible with simple dissection

Shell removal by severing pedal-retractor muscle shows muscle-bundles clearly 23Pd flic.kr/p/AzykaY ; anterior bundle on each side is largest and strongest as must firmly pull down shell further to anterior where bundles are absent. Removal of viscera reveals that muscle bundles continue far into foot 24Pd flic.kr/p/BdwNkP towards median groove of large blood-sinus 25Pd flic.kr/p/ABS7Sp . Shell removal exposes entire mantle 23Pd flic.kr/p/AzykaY subdivided into a) pale translucent mantle-skirt, b) narrow black band over pallial-groove containing gills, c) large black amphora-shaped area, often with pale vertex patch, over viscera and d) separated from amphora by pale anterior-mantle attachment, smaller black area over the nuchal cavity containing the head and anterior pallial gills 26Pd flic.kr/p/BciErS . Pale patch within black amphora may be related to excavated patch near shell-vertex, see 11Pd flic.kr/p/Bd4YEr , a feature frequently found on P. depressa. If mantle skirt is folded back, 26Pd flic.kr/p/BciErS , collapsed pallial gills exposed. Careful removal of black amphora area of mantle reveals translucent membrane over viscera 27Pd flic.kr/p/AzysF8 ; when removed, clear view, 28Pd flic.kr/p/BbdZum , of digestive gland, intestine and rectum. Efferent pallial vessel in mantle-skirt, 26Pd flic.kr/p/BciErS carries blood from mantle to right of nuchal cavity 29Pd flic.kr/p/AguVDE and through it to elongated heart behind left of cavity 30Pd flic.kr/p/Bex7R6 . When roof of nuchal cavity folded back, translucent white head showing purple-red of internal odontophore visible 26Pd flic.kr/p/BciErS . Removal of head's epithelium reveals odontophore and anterior of radula with hyaline shield 28Pd flic.kr/p/BbdZum . Removal of viscera reveals entire long radula, folded and coiled to fit in body 24Pd flic.kr/p/BdwNkP . P. depressa probably has longest radula relative to shell-length, up to 270%, of any British mollusc 31Pd flic.kr/p/BbdUdE (Fretter & Graham, 1962, p.172). Fully mineralized, golden radular teeth, ready for action, clearly visible at anterior where radula rests on transparent hyaline shield on top of odontophore 32Pd flic.kr/p/Bcivym . Inner lips enclosed at sides and anterior by white chitinous unarticulated jaw# 24Pd flic.kr/p/BdwNkP . White, cuticularized, triangular licker at tip of radula is divided into plate-like ridges by deep transverse grooves 32Pd flic.kr/p/Bcivym . Teeth obscured by white translucent radular sac to posterior of hyaline shield. When radular sac removed by treatment with 10% solution NaOH, posterior of radula clearly seen to have white ribbon with slightly pigmented teeth as mineralization at early stage 33Pd flic.kr/p/ABRUWR while further forward ribbon is rich crimson, and teeth strongly pigmented golden with strong hard minerals of iron and silica. Each row of teeth arranged in docoglossan formula, 3+D+2+R+2+D+3: at centre, two pairs of large, unicuspid, pigmented lateral teeth (with small, unpigmented rachidian/median tooth hidden from easy view at their base), and near each margin of ribbon a single, tricuspid, pigmented, dominant-marginal tooth with, close-by, three inconspicuous, unicuspid, marginal teeth 33Pd flic.kr/p/ABRUWR . Middle cusp of dominant-marginal on P. depressa and P. vulgata is largest; on P. ulyssiponensis outer cusp largest. Before and during spring-autumn breeding season, large gonads (20% of female's mass) occur in mature adults between viscera and foot and, when fully developed, spread up around periphery of visceral mass 30Pd flic.kr/p/Bex7R6 . Male testes are pinkish/orange/yellow with numerous interconnected tubules seen side-on 34Pd flic.kr/p/ABRUor or end-on 35Pd flic.kr/p/BbdNHb . Female gonads not observed by IFS (four adults dissected in late September; two with testes, two without gonads- spent females?) but as reproductive systems similar in the genus, probably greenish and granular as in P. vulgata .

SPECIES DESCRIPTION part B at 2Pd flic.kr/p/AfbFkR

GLOSSARY

 

amphora – (on interior of limpet shell) Roman amphora-shaped area enclosed by scars of pedal-retractor muscle and anterior mantle-attachment.

 

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

apex - earliest formed part of a gastropod shell, the summit of the cone. (In this limpet-account restricted to the exterior of the shell, and “vertex” used for the interior.)

 

cephalic – (adj.) of or on the head.

cilia – (pl.) microscopic linear extensions of membrane that move in rhythmic waves to create locomotion, or move particles and liquids e.g. inhalent water currents. (“cilium” singular). (Electron scanning microscope image at flic.kr/p/qQB5zj )

 

ciliary – (adj.) relating to or involving cilia.

coll. – in the collection of (named person or institution) (compare with legit).

conoid – shaped like a cone.

ctenidium – comb-like molluscan gill; usually an axis with a row of filaments either side (missing from Patella spp.).

distal - away from centre of body or point of attachment.

ditaxic - (of locomotion waves on foot) double series of waves, out of phase with each other, one series on each side of median line on sole.

 

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

EHWS - extreme high water spring tide level (usually near March and September equinoxes).

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

 

epithelium – membranous covering of internal and external surfaces of animal's body, e.g. skin and lining of tubes and cavities.

 

head scar – term used by many British authors for patch of different shell-material, and often different colour, near vertex of interior of limpet shell; misnomer as the mobile head, free of any attachment to the shell or mantle-roof of the nuchal cavity cannot make a scar. A preferable term is “vertex patch”.

 

height – (of limpet) perpendicular distance from apex to plane of aperture-rim (best measured with callipers).

 

hyaline shield – transparent sheet of chitin at anterior of radula that rests on bolsters of odontophore; attachment point for retractor muscles of radula; helps guide food particles into mouth.

 

interspecific – existing or arising between different species.

intraspecific – occuring within a single species or involving members of one species.

jaw - unarticulated chitinous structure that encloses inner lips of Patella spp. at sides and anterior.

 

legit – (abbreviation; leg.) collected/ found by (compare with coll.)

licker - cuticularized structure with plate-like ridges and deep transverse grooves at tip of radula of Patella spp.; retains and sweeps up food particles.

 

mantle – sheet of tissue covering visceral mass of molluscs. Secretes shell of shelled species, and forms part or all of dorsal body surface (notum) of those without shells. (See mantle skirt.)

 

mantle skirt – extension on gastropods of mantle proper as a flap roofing a cavity containing gills, genital and renal openings, anus etc. On limpets, skirt and cavity extend around periphery of animal.

 

MHWN - mean high water neap tide level (mean level reached by weakest high tides for a few days every fortnight. i.e. those that rise the least).

 

MLWN – mean low water neap tide level (mean level reached by weakest low tides for a few days every fortnight. i.e. those that fall the least).

 

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).

 

nuchal – (adj.) of nape of the neck.

nuchal cavity – cavity roofed by mantle skirt that contains head of limpet; part of mantle cavity (remainder consists of pallial groove on each side of body).

 

ovoid – egg-shaped, as a solid or in outline.

pallial groove band – shell material deposited on interior of shell by strip of black mantle roofing the pallial groove that contains the gills. On British Patella spp. it is often clouded-white.

pedal retractor muscle – strong muscle that retracts foot into shell of most gastropods, but on limpets is used to clamp shell to substrate, a.k.a. “foot muscle”.

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

scar – mark on shell made by attachment point of muscle or other body part.

skirt shell layer - shell material deposited on interior of shell by mantle skirt. On British Patella spp. colourless when deposited, and clouded white, or transparent showing the colours of the outer layer. Crystalline structure causes short lines of blue iridescence parallel to the aperture rim on all four British species of Patella when the light is right.

 

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.

 

tricuspid - (of tooth) having three points.

unicuspid - (of tooth) having a single point.

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

 

vertex – angle at highest point on interior of limpet-shell. [Synonym of “apex”, chosen (by IFS) to help avoid confusion with the highest point, apex, on the exterior. Gmelin used “vertex” when describing the interior of Patella ulyssiponensis, and in classical Latin “vertex” was used for the “pole of the heavens”; obviously only seen from below.]

 

vertex patch –layer of different shell-material, and often different colour, at vertex of interior of limpet shell. (See “head scar”.)

 

Done