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(Linné, 1767)

Description:
Shell fragile and thin. Equivalve; inequilateral, outline roughly triangular. Dorsal margin is straight, ligament thin, inconspicuous, lying along the anterior half of margin; ventral margin is straight anteriorly, becoming concave or irregular posteriorly, grading into rounded posterior margin. Valves are gaping posteriorly and along anterio-ventral margin. Sculpture of fine concentric lines and variable number of smooth, wavy ridges radiating from umbones, raised dorsally and posteriorly into delicate, flat spines. Interior of shell is glossy, anterior adductor scar is small, hidden beneath umbone, posterior large and distinct, in the middle of valve. A number of vertical ridges, or septa, closely packed, may be seen beneath umbones at anterior end of shell.

Size:
Up to 37 x 20 cm.

Colour:
Yellow-horn to darker brown, occasionally with few darker patches. Periostracum is thin.

Animal:
Gregarious in habit, found in some numbers together. The animal, which varies in colour from yellow to red-brown, uses its foot chiefly for spinning the strong and abundant byssus by which it moors itself to the bottom. The foot is dwindled to small proportions due to the inactivity of the animal.

Habitat:
Offshore, in mud, sand or fine gravel; lives with the pointed anterior end deeply buried and attached by a byssus emerging from the ventral gape. From LWM to 150 m depth.

Distribution:
Not common. Predominantly southern and western; as far north as Orkney (Distr. A. pectinata).

Atrina pectinata