Corbula gibba

(Olivi, 1792)

Description (shell):
Shell thick, broadly oval to subtriangular, umbones close to midline; right valve convex, enclosing and overlapping left, its ventral margin covered only by a fringe of periostracum from the left valve. Sculpture of coarse concentric grooves and ridges, and a few radiating striae on left valve. Right valve with a single, massive tooth, anterior to a recessed, triangular chondrophore, and single elongate anterior and posterior lateral teeth. Left valve with a shallow chondrophore posterior to a deep socket, no lateral teeth. Adductor scars and pallial line usually clear, pallial sinus very shallow (C. gibba-drawing).

Up to 15 mm long.

Dull white to cream; periostracum coarse, grey-brown, usually worn at the umbones, most conspicuous on left valve. Inner surfaces white or yellowish, sometimes tinted blue.

The animal has a comparatively large and thick foot, which it uses for burrowing just below the surface. The shell is drawn out behind to make a cover for the siphons, which are so short as to be only slightly protruded (C. gibba-animal).

In muddy sand and gravel, occasionally on the lower shore, most abundant offshore.

Distributed from Norway south to the Mediterranean and west Africa (Distr. C. gibba). Also found in the enclosed Lake Grevelingen in SW Netherlands.