Anomia ephippium

Linné, 1758

Shell brittle, fragile, roughly circular, the posterior margin frequently bluntly produced; often rather irregular when attached to an uneven substratum. Left valve convex, often deeply cupped and overlapping the right valve (A. ephippium-drawing); with three distinct scars on inner surface, in an oblique line, in concavity of shell (A. ephippium-inside). Right valve thin, flat, or irregularly concave, with elliptical byssal aperture dorsally; single adductor scar postero-ventral to byssal aperture. Sculpture of wavy concentric lines, often raised as irregular scales. Growth stages usually clear, except in older shells when they may be obscured by incrustations or, on the left valve, worn smooth.

Up to 60 mm.

Colour white or grey, occasionally with a pink or bluish tinge.

Varies in colour from yellow to red and brown. As the animal lives usually solitarily attached to the underlying surface, it can develop its shell pretty equally in all directions; the mantle follows the outline of the shell and is therefore more or less circular, its margins fringed with two or three rows of yellowish filaments. The white cylindrical foot is very small.

From the lower shore to at least 150 m and perhaps to the edge of the continental shelf. Attaches to various hard substrata, including other molluscs, and to algal holdfasts.

Widespread and common on hard substrata (Distr. A. ephippium). Occurs also in the Mediterranean; distributed from Iceland to West Africa, and to the South Atlantic Islands.