Mercenaria mercenaria


Description (shell):
Shell subtriangular, thick; umbones prominent, anterior to midline. Sculpture of numerous thin concentric ridges, sharp and raised on early growth stages, and close to anterior or posterior margins, but usually worn smooth on central areas of larger shells. Growth stages clear. Lunule deeply impressed, heart-shaped, finely striated; escutcheon elongate, narrow, poorly defined. Three conspicuous cardinal teeth in each valve, with a group of small corrugations behind posterior tooth. Adductor scars and pallial line distinct, pallial sinus short, triangular; inner margin very finely crenulate.

Up to 120 mm long.

Light brown to grey, often in varying concentric bands; periostracum thin, greyish. Inner surfaces glossy white, often with deep bluish-purple tints posteriorly or about the muscle scars.

The foot is large and tongue-shaped, adapted in burrowing. The siphons are unequal, cylindrical and relatively short.

In mud, from the lower shore into the shallow sublittoral.

The North American edible clam, or Quahog, has been introduced into British waters, deliberately or otherwise, on several occasions since the middle of the last century. Populations may still be found at several points on the south and south-east coasts, most notably in Southampton water and the Solent, and at Burnham-on-Crouch (Distr. M. mercenaria).