(Montagu, 1803)
Description (shell):
Shell thin and brittle, subtriangular; umbones prominent, with the hinge line sloping away evenly on each side. Sculpture of numerous fine concentric lines, growth stages visible with hand lens. Chondrophore slender, posteriorly directed. Right valve with two short cardinal teeth anterior to chondrophore and single, elongate anterior and posterior laterals; left valve with one small cardinal tooth and single, poorly developed, anterior and posterior laterals. Adductor scars and pallial line usually distinct; pallial sinus deep, its lower edge partly fused with pallial line. Cruciform muscle scars obscure (A. tenuis-drawing).
Size:
Up to 13 mm long.
Colour:
Dull white, with a pale grey or brown periostracum. Inner surfaces white.
Animal:
White, with a delicate fringe to the mantle. The inhalent tube is twice the length of the shell, the exhalent tube 1/3 or less.
Habitat:
Burrows in soft substrata, in estuaries and tidal flats subject to fluctuating salinity. Intertidal only.
Distribution:
Reported in the North Sea as far north as Northumberland and the German Bight (Distr. A. tenuis). Distributed south to the Mediterranean and north-west Africa.