Montacuta substriata

(Montagu, 1808)

Description (shell):
Shell thin and fragile, obliquely oval, umbones posterior to midline. Ventral margin often slightly concave medially. Sculpture of fine concentric lines and few low, radiating ribs. Growth stages clear. Each valve with single anterior lateral tooth only. Adductor scars clear, anterior slightly larger, pallial line wide and diffuse (M. substriata-drawing).

Up to 3 mm in length.

White, with inconspicuous pale brown periostracum. Inner surface of shell white.

Almost transparent. The animal spins a byssus, and on the lower margin of the shell there is an indentation from which this issues. The rear portion of the fringed mantle forms a brief tube for the outward current of water. The foot is large and powerful.

Lives in association with sea urchins, usually attached to the anal spines. Recorded from various localities, associated with Spatangus purpureus and Echinocardium flavescens. Distributed from ELWS, offshore to about 100 m.

Ranges from Norway to the Mediterranean (Distr. M. substriata).