Spisula subtruncata

(da Costa, 1778)

Description (shell):
Shell thick and strong, subtriangular but distinctly asymmetrical; umbones close to midline, posterior hinge line and margin sloping more steeply than anterior, posterior end appearing slightly drawn out. Sculpture of fine concentric lines and grooves, growth stages clear. Lunule and escutcheon broad and elongate, latter bounded by low ridges extending from umbones. Right valve with two short cardinal teeth and paired, elongate anterior and posterior laterals. Left valve with three cardinal teeth; anterior two forming a single forked structure extending almost to edge of the hinge plate, third very small, indistinct; with single elongate, anterior and posterior laterals. Interlocking surfaces of lateral teeth serrated. Chondrophore posterior to cardinal teeth. Adductor scars and pallial line distinct, pallial sinus broad and rounded, extending to a point below and behind the midline of the posterior lateral teeth (S. subtruncata-drawing).

Up to 30 mm long.

Dull white to cream, periostracum greyish brown. Inner surfaces glossy, white (S. subtruncata).

The animal has a mantle with toothed edge. The siphons are short, their mouths fringed with yellow or red filaments; united throughout their length, but the exhalent tube is fitted with a tubular valve. The yellowish foot is slender.

Burrowing in muddy or silty sand, from the lower shore into the shallow sublittoral.

Widespread in the whole North Sea (Distr. S. subtruncata); distributed from Norway to the Mediterranean and Canary Isles.