(Linné, 1758)
Description (shell):
Shell thick and strong, approximately rhombic in shape: hinge line sloping gently from umbones on each side, posterior margin scarcely convex, almost straight, anterior margin more strongly convex. Sculpture of 18-20 bold ribs and fine concentric grooves and ridges. Dorsally, each rib has a central keel, bearing short pointed spines; ventrally the keel is obscured and spines appear separate. Growth stages clear. Two cardinal teeth in each valve; right valve with two anterior and one posterior lateral teeth, left valve with single anterior and posterior laterals. On the inner surface, the pallial line and adductor scars are distinct. External sculpture visible as grooves extending from ventral margin to pallial line, fading rapidly beyond it and smooth beneath umbones (A. tuberculata-inside).
Size:
Up to 90 mm long.
Colour:
Off-white, yellow, or light brown, often in concentric bands of different shades, frequently darker about umbones. Periostracum thin, yellowish. Inner surface white, glossy ventrally, becoming dull beneath the umbones (A. tuberculata-drawing).
Animal:
The gills are long and much folded back. The siphons are rather long. The foot is large, long and cylindrical. The mantle margins are jagged. Pigment spots serving as visual organs are scattered over the margins of the mantle and over the siphons (A. tuberculata-animal).
Habitat:
On muddy sand and gravel, from the lower shore into the shallow sublittoral.
Distribution:
Southern part of the North Sea only (Distr. A. tuberculata), ranging south to the Mediterranean and north-west Africa.