Macoma balthica

(Linné, 1758)

Description (shell):
Shell broadly oval, umbones more or less on midline; anterior hinge line and margin regularly convex, posterior hinge line and margin slightly attenuated. Sculpture of numerous, fine, concentric lines; growth stages clear, usually marked by bands of colour. Two small cardinal teeth in each valve, the right posterior and left anterior being bifid. No lateral teeth. Adductor scars and pallial line distinct, cruciform scars unclear; pallial sinus irregular, deep, lower edge largely fused with pallial line (M. balthica-drawing).

Up to 25 mm long.

Colour very variable: white, yellow, pink, or purple, in various shades, unicolorous or banded. Periostracum light brown, most conspicuous at margins. Inner surfaces glossy; white, pink, or purplish.

Animal is yellowish, tinged with brown. Long, separate siphons, the upper siphon is larger than the lower. Foot is powerful. Mantle fringed with tentacles.

Burrows in soft substrata, particularly in estuaries and on tidal flats, where it may be abundant; intertidal only.

Distributed from the White Sea south to Spain and Portugal (Distr. M. balthica).