not all genera (for an exception, see the genus Laevicardium, the egg cockles, which have very smooth shells).

The shell of a cockle is able to close completely (i.e., there is no "gap" at any point around the edge). Though the shell of a cockle may superficially resemble that of a scallop because of the ribs, cockles can be distinguished from scallops morphologically in that cockle shells lack "auricles" (triangular ear-shaped protrusions