Abra alba

(Wood W., 1802)

Description (shell):
Shell thin and brittle, broadly oval, umbones posterior to midline. Sculpture of very fine concentric lines, growth stages clear. Chondrophore elliptical, posteriorly directed. Two small, peg-like cardinal teeth anterior to chondrophore in right valve, a single one in left valve; single, thin anterior and posterior lateral teeth in right valve, present but less prominent in left. Adductor scars and pallial line clear, cruciform muscle scars visible with hand lens. Pallial sinus deep, rather irregular (A. alba-drawing).

Up to 25 mm long.

White and glossy; periostracum thin, apparent only at margins. Inner surfaces white.

Whitish tinged with blue and spotted with pure white. The two siphons are as long as the shell; the mantle is edged with several rows of minute fleshy points.

Burrows in groups in soft substrata; occasionally on the lower shore but most abundant in shallow, offshore waters (to about 60 m) where it may be a dominant member of the benthic infauna.

Widespread in the North Sea (Distr. A. alba); distributed from Norway to the Mediterranean and west Africa.