Pecten maximus

(Linné, 1758)

Description (shell):
Shell thick and solid; inequivalve, left valve flat, right valve strongly convex, slightly overlapping the left along its margin. Equilateral, with a small byssal notch in the right anterior ear. Ears equal. Both valves with bold, radiating ribs, about 16 in number, distinctly quadrate in section on left valve, but more rounded on right. Finer radiating ridges on both ribs and intervening grooves, concentric sculpture of corrugated lines, growth stages clear. Ears with numerous fine ridges. External sculpture discernible over most of the shell on inner surfaces (P. maximus-drawing 2).

Up to 150 mm long, slightly longer than deep.

Right (convex) valve off-white, yellowish, or light brown, often with bands or spots of darker pigment, left valve light pink to reddish brown; periostracum dirty brown. Inner surfaces of shell nacreous, often with patches or streaks of dark or light chestnut (P. maximus-drawing).

The animal is pink or red, the mantle marbled with brown and white. Lives attached by a byssus when young, later free and capable of swimming by the opening and rapid closing of the valves. The muscle for closing the valves is very large and powerful. The foot is developed as a finger-like organ, occupied in the spinning of byssal threads, which pass through the ears. The mantle margin is double, the inner finely fringed and the outer edged with long tentacles, and at their base gleam a row of 30-35 large, greenish or dark blue, unequal ocelli (eye-spots) in two series.

Lives in depression in sand or fine gravel with left valve uppermost, offshore to about 100 m.

Distributed from Norway to the Atlantic coast of Spain, common in the whole North Sea (Distr. P. maximus).