Lasaea rubra

(Montagu, 1803)

Description (shell):
Shell thin and fragile, obliquely oval, tumid, both valves strongly convex; inequilateral, umbones posterior to midline. Sculpture of numerous, closely spaced, fine, concentric lines, a few faint radiating striae may be present; growth stages clear, raised. Right valve with single anterior and posterior lateral teeth, left valve with one small cardinal tooth and single anterior and posterior laterals; in both valves position of the internal ligament is marked by deep embayment below hinge line and broad plate below posterior lateral tooth. Adductor scars relatively large, pallial line broad and ill-defined (L. rubra-drawing).

Up to 3 mm in length.

Colour white, with concentric bands of pale pink or red, darkest towards margins; periostracum light yellow-brown. Inner surface white.

The mantle extends beyond the shell forming a protuberant incurrent tube in front. The excurrent orifice is not seen beyond the shell margin. Moves freely by means of its long, tongue-shaped foot. A byssus moors the animal to the substratum. This species retains its eggs until they are hatched. These are produced in batches of 12-20, and when sufficiently developed they are shot out through the incurrent siphon.

An intertidal species, common on rocky shores all around the British Isles. Attached by a byssus, it is found in crevices, among Fucus clumps or in Lichina tufts; often present in very large numbers.

Distributed from Norway to the Mediterranean and the Canary Isles (Distr. L. rubra).