(Müller O.F., 1776)
Description (shell):
Shell is thin, fragile, inequilateral, the anterior ears three or four times as long as the posterior. Inequivalve, a large byssal notch in the right anterior ear. Circular in outline, except for the projecting ears. Sculpture of valves different: right valve with fine radiating and concentric lines, its surface smooth except for small spines which sometimes occur near the margins; left valve rough, with numerous, very fine, radiating ribs carrying small spines. Growth stages are clear. Byssal notch with teeth. Margin is smooth.
Size:
Up to 19 mm in length.
Colour:
Colour variable but mainly white, pink and red-brown gathered into a variety of stripes, zigzags, blotches, etc.
Animal:
The whitish animal lives attached by a byssus when small, later free and capable of swimming by the opening and rapid closing of the valves. 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 25 crimson pupilled, blue-black ocelli (eye-spots), of unequal size and irregular disposition (P. striatum-animal).
Habitat:
Around the British Isles this bivalve lives offshore, to considerable depth, generally on coarse bottoms of muddy sand, gravel or shell.
Distribution:
Distributed from southern Iceland and northern Norway to the Iberian Peninsula and the western Mediterranean, not in the southern North Sea (Distr. P. striatum).