(da Costa, 1778)
Description (shell):
Shell thick and robust, broadly oval, prominent umbones imparting subtriangular outline. Lunule and escutcheon distinct, deep; ligament visible in anterior half of escutcheon. Sculpture of bold concentric ridges, growth stages indiscernible. Left valve with two prominent cardinal teeth below umbones and a third, slender, indistinct and often abraded, extending below ligament. Right valve with very thick anterior cardinal tooth and slender one posteriorly; additionally, slender ridge below escutcheon may be taken for posterior lateral tooth. Adductor scars and pallial line very clear, inner shell margin distinctly crenulate, rarely smooth (A. sulcata-drawing).
Size:
Up to 30 mm long.
Colour:
Usually white (rarely pink) with thick, mid- to dark-brown periostracum, often encrusted and stained black about umbones. Inner surface of shell dull white, often with pink or brown tinge.
Animal:
Body almost round, flattened from the sides. The lips are large; the mantle is thick, not fringed with tentacles, but part of it forms a short excretory siphon behind. The foot is conical and small, though powerful.
Habitat:
In mud or fine gravels with sand, shells, or mud, offshore.
Distribution:
Distributed from southern Arctic waters to the Mediterranean and north-west Africa (Distr. A. sulcata).