Pododesmus patelliformis (Linnaeus, 1761)Anomioidea : Anomiidae
To size: To 40mm. Shell Structure: Upper valve thin but not fragile; lower valve very thin, hyaline. Equivalve: Inequivalve, upper (left) valve convex; lower (right valve) flat. Equilateral: Inequilateral, beaks close to the middle of the dorsal margin. Outline: Upper valve subcircular, but irregular, conforming to attachment surface; lower valve as upper but with a large oval byssus aperture.
Sculpture: Upper valve densely wrinkled with a variable number (20-60) of weak radial riblets, these irregular and often interrupted; lower valve with growth lines only. Margin: Irregular but smooth. Ligament: In a half moon shaped pit beneath the beaks. Hinge: Obscure, some with traces of a median crural ridge directly above the ligament. Pallial Musculature: Upper valve with two distinct scars the dorsal (byssus retractor) much larger and separated (patelliformis state) from the smaller single adductor scar; often scars coalesce (squama state). Scars with faint radiating furrows. Lower valve with a single faint adductor scar. Periostracum: Obscure. Colour: Upper valve pale tan to brown, some showing green through the central area and with brown between the ribs on the margins; often obscured by attached epifauna, internally the central area tinged green to yellow green. Lower valve white, semitransparent. Additional Characters: Anatomy: Ctendium with reflected filaments.
Distribution & Ecology
Attached by its byssus to rocks and hard substrates from the intertidal and sublittoral. It is widely recorded from shelf depths to the shelf edge but this may include many records of the striated form of P. squama (see Comments).
Continental Shelf (to 200m)
Juveniles & Similar Species
Key Features & Similar Species
From A. ephippium by the presence of only two muscle scars instead of three. See Comments for our views on the status of P. squama.
Smith & Heppell (1991) regard P. patelliformis and P. squama to be varieties of the same species and therefore include only P. patelliformis in their list. At this time we agree that the muscle scar character used to separate the nominal taxa does not hold but we have observed that offshore shells may have a different sculpture from sublittoral and intertidal shells. This striated form was described by Lovén as P. striata and this form is included in the synonymy of P. squama by CLEMAM. Under P. squama we describe this striated form only.
Listed are literature citing Pododesmus patelliformis (Linnaeus, 1761). Reference containing the species Type Description is highlighted.
Linnaeus C 1761. Fauna Svecica sistens animalia Sveciæ Regni: mammalia, aves, amphibia, pisces, insecta, vermes. natalium, descriptionibus insectorum. Editio altera, auctior. - natalium, descriptionibus insectorum. Editio altera, auctior–- Stockholmiæ, Laurentii Salvii. 578pp, 1pl.
Winckworth, R I922. Note on the British species of Anomia. Proceedings of the Malacological Society of London. 15: 32-34.
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