Mytilus edulis

Linné, 1758

Description (shell):
Shell solid, equivalve; inequilateral, beaks at the anterior end. Shell approximately triangular in outline. Hinge line without teeth, but with 3 to 12 small crenulations under the umbones. External ligament much concealed, extending more than half-way from the beaks to the highest point of the shell. Sculpture of fine concentric lines; growth stages clear. Pallial line wide; anterior adductor scar very small, posterior one large. Margin smooth.

Length variable: commonly 50-100 mm, although many populations rarely reach 30 mm, and largest shells up to 150-200 mm.

Colour light horn to blue or purple, dark purplish blue when older; small specimens often marked with pale blue and brown rays on a translucent ground. Periostracum thick, deep blue to black, occasionally dirty brown, glossy where new, often abraded over much of the anterior end. Inner surface of shell white below ligament, progressively blue and dark, towards a deep purplish black posterior margin (M. edulis-drawing).

The mantle has a double margin, the outer one plain, the inner is at different parts fringed or toothed and on the hinder part formed into an imperfect siphon. Colour of the mantle edge of living specimens is typically yellow-brown. Strongly gregarious in its habits. Widely cultivated and used as food.

Attached by a byssus issuing ventrally, close to umbones, M. edulis occurs in dense beds from upper shore and into the shallow sublittoral (M. edulis bed).

Widespread and common in the whole North Sea (Distr. M. edulis). It ranges from Arctic waters south to the Mediterranean.