Musculus niger

(Gray J.E., 1824)

Description (shell):
Shell thin, brittle, broadly oval in outline, ventral margin more or less straight. Umbones subterminal, anterior margin extending well beyond beaks; umbonal ridges not pronounced, grading gently into rest of shell. About 12-15 delicate radiating ribs anteriorly, 40-60 posteriorly, fine concentric lines also present; ribbed areas with finely crenulate margins, appearing decussate when viewed with a hand lens, growth stages clear. External sculpture visible on inner side.

Up to 50 mm long.

Shell light tan to deeper brown, with a paler greenish area ventrally between the two ribbed areas; periostracum light brown or olive to deep brown or almost black in large specimens. Inside of shell pale bluish white, with some darker tinges (M. niger-drawing).

The mantle forms a distinct incurrent tube in front and an excurrent one behind. The foot is strap-shaped and may be extended until it is a mere thread two or three times the length of the shell.

Occurs offshore, on sandy mud and fine gravel.

Northern distribution. Absent from the southern North Sea (Distr. M. niger).