Mya arenaria

Linné, 1758

Description (shell):
Shell thick and strong, oval, umbones just posterior to midline; anterior end regularly rounded, posterior somewhat tapered. Sculpture of fine concentric lines, becoming coarser and more corrugated close to margins, also a few, faint, radiating striae. Growth stages clear. Left valve with a prominent spatulate chondrophore, projecting at a right angle to hinge line, with a distinct tooth-like ridge along its posterior edge. Right valve with a concave, spatulate chondrophore recessed beneath umbo. Adductor scars and partial line distinct; anterior scar elongate, posterior rounded (M. arenaria-drawing 2).

Up to 150 mm long.

Off-white, yellowish, or fawn, dark greyish brown about the umbones; periostracum light brown, often stained by iron deposits. Inner surfaces white (M. arenaria-drawing).

The siphons are connected throughout their total length and though they may be completely withdrawn into the shell, they are usually fully extended. This has caused the hinder end of the shell to gape widely. These animals are deep burrowers and the foot is positioned downwards, while the siphons reach straight up through sand or mud to the water above (M. arenaria-animal).

In sand, often mixed with mud or gravel, on the lower shore and offshore to about 20 m. Often very common in estuaries, where it may occur in extensive beds.

Circumboreal, not reaching the Mediterranean (Distr. M. arenaria).