(cockles), a family of bivalve mollusks having a strong, ribbed, heart-shaped shell reaching 10 cm in length. The Serripes groenlandicus is among the largest of the approximately 250 widely distributed species. Cockles inhabit seas and brackish waters; they are found in all the seas of the USSR. The most common species, Cerastoderma edule, is 5–6 cm long. It is distributed along the western and northern coasts of Europe and in the Baltic, Mediterranean, Black, Caspian, and Aral seas; it entered the two last seas when they were connected with the Black Sea. C. edule and a few other species have commercial significance.