(Scacchi, 1834)
Description (shell):
Shell brittle, slightly inequivalve, the left valve a little more convex than the right one. Inequilateral beaks behind the midline, directed inwards. Broadly oval in outline, the anterior dorsal margin sloping downwards, slightly rostrate posteriorly. External ligament is a small brown arched band behind the beaks, the internal ligament is in an oblique chondrophore below it. Sculpture of fine concentric lines and faint radiating lines (the latter are frequently worn away). Growth stages are clear. Right valve with two short cardinal teeth and long single anterior and posterior laterals; left valve with one short cardinal tooth and single, weak, anterior and posterior laterals. Anterior adductor scar longer and thinner than the posterior one. Cruciform muscle scars obscure. Pallial sinus deep, its lower border partly confluent with the pallial line. Margin is smooth.
Size:
Up to 19 mm in length.
Colour:
White. Periostracum brown.
Animal:
Foot is large and powerful; two long siphons.
Habitat:
Burrows in soft substrata.
Distribution:
Only in the northern parts of the North Sea (Distr. A. longicallus). It is distributed from the Norwegian Sea, south to the Iberian Peninsula into the Mediterranean, along the Atlantic coast of Morocco and to the Azores.