Shell is thin, equivalve and equilateral. Ears are small and equal. Regularly oval in outline, except for the slightly protruding ears. Beaks apart exposing a wide cardinal area with a broadly based central triangular ligament pit (resilifer). Sculpture of 24 radiating ribs, of which the central one is slightly wider, and concentric lines; ribs are not present on the ears or nearby lateral areas of the valves. Growth stages are clear. Inside of shell with lines showing through from the external ribbing and a central groove which is the reverse of the larger external rib. Margin is crenulate where it is cut by the ribs.
Up to 6.3 mm from anterior to posterior margin.
Beneath a cream periostracum the shell is white.
White. The tentacles which fringe the mantle are exceedingly long and numerous. Ocelli (eye-spots) are present, but inconspicuous. The foot is finger-shaped and grooved. The lips are furnished with tentacles like those of the mantle. Uses the foot for crawling.
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. Lives off shore, from 3.7 m to considerable depth, preferring bottoms of mud, sandy mud, gravel and sandy gravel.
Collected off Plymouth, the Isle of Man and the west coast of Scotland and is distributed from south-west Greenland, Finmarken, the Faroes, Iceland, south to the Mediterranean, and to the Canary Isles and down the eastern seaboard of North America to Puerto Rico. In the Pacific it occurs from Alaska to Mexico (Distr. L. subauriculata).