Limatula gwyni

(Sykes, 1903)

Shell thin, equivalve and equilateral. Ears are small and about equal. Outline is regularly oval. The shell has a sculpture of 30-40 radiating ribs crossed by fine concentric lines and ridges. Ribs are not present on the ears or nearby marginal areas. In the centre of each valve one rib is often, but not always, a little wider or more prominent than the others and on the inside of each valve in these regions there is always a channelled groove, the reverse effect of a wider external rib. Bordering this groove on the inside of the shell there are always radiating lines reflecting the external ribbing. Growth stages are clear. Margin is crenulate where it is cut by the ribs. The interior of the valves is covered by a thick layer of mother-of-pearl (L. gwyni-2).

Up to 13 mm long.

Beneath the dirty white or cream periostracum the shell is translucent, the single muscle scar being visible from the outside.

The tentacles which fringe the mantle are exceedingly long and numerous. Ocelli (eye-spots) are present, but inconspicuous. The body and foot are pale orange, the tentacles are more pink in hue. The foot is finger-shaped and grooved. The lips are furnished with tentacles like those of the mantle.

During early life shells flit through the water like scallops. Shells may temporarily attach themselves by an easily detachable byssus, or they form a nest in which are several youngsters or one adult. On muddy bottoms between 20-2000 m deep.

Cosmopolitan. All along the European coasts south to Guinea, West Africa (Distr. L. gwyni). In the western Atlantic from the Arctic south to the Gulf of Mexico. Also reported from Japan and the Mediterranean.