(Montagu, 1803)
Description (shell):
Shell thick, oval; beaks just anterior to midline, pointed and extending anteriorly. Dorsal margin anterior to umbones concave, with a distinct oval lunule; ligament visible in deep fusiform escutcheon bordered laterally by erect, flared, and crenellated rims. Sculpture of numerous fine, closely spaced, concentric ridges; growth stages unclear. Right valve with single cardinal tooth, and single anterior and posterior lateral teeth. Left valve with two cardinal and single anterior and posterior lateral teeth, but in addition ridges may be developed along hinge line and appear as extra laterals. Pallial line distinct on inner surface; anterior adductor scar elongate-oval, roughly dumb-bell shaped, touching the pallial line along its anterior ventral border (M. spinifera-drawing).
Size:
Up to 25 mm long.
Colour:
White or cream with an indistinct, pale beige periostracum. Inner surface of shell white.
Habitat:
In mud and muddy sands, offshore to about 100 m.
Distribution:
Ranges from Norway to the Mediterranean and the Azores (Distr. M. spinifera ).