Adacna

Adacna is a genus of fresh- and brackish-water bivalve molluscs of the cockle family (Cardiidae). It includes species characterized by thin shells, with flattened ribs and usually rather deep pallial sinus. The four extant species are found in fresh- and brackish-water lakes of the Danube Delta, estuaries (limans) of the north-western Black Sea, the Taganrog Bay of the Sea of Azov and the Caspian Sea. Two Caspian species were also present in the Aral Sea, where they went extinct by the end of the 1970s as the lake was shrinking and became more saline. Two fossil species have been described from the Pleistocene deposits of the Caspian Sea region and one species is only known from the Late Pleistocene of south-eastern Turkey.

These bivalves are mobile filter feeders that live on silty, sandy and sandy-silty bottoms and usually fully burrow into the sediment, leaving their long and fused siphons on the surface. They feed on suspended detritus and unicellular algae, but are also able to consume food particles on the sediment surface.