(Montagu, 1803)
Description (shell):
Shell thin and fragile, oval, the umbones are posterior to midline. Sculpture of fine, closely spaced, concentric lines; growth stages are clear. Each valve with a single anterior and single posterior lateral tooth. Adductor scars are about equal, distinct; pallial line is broad.
Size:
Up to 3 mm long.
Colour:
White or translucent, periostracum light brown or olive. Inside of shell is white.
Animal:
The mantle has its margin fringed and forms a very brief tube behind. The large broad foot is somewhat triangular in outline.
Habitat:
From ELWS to about 100 m, in muddy sand or fine gravel, in crevices of dead oyster valves, in the burrows of the sipunculid Golfingia , or associated with the ophiuroid Acrocnida brachiata .
Distribution:
Common in the whole North Sea (Distr. M. bidentata), it ranges from Norway to West Africa and the Mediterranean.