The use of bivalve shells by the shellback crabs Hypoconcha arcuata Stimpson, 1858 and H. parasitica (Linnaeus, 1763) (Brachyura: Dromiidae: Hypoconchinae) in southeastern Brazil

We describe the use of abraded bivalve shells by the shellback crabs Hypoconcha arcuata Stimpson, 1858 and H. parasitica (Linnaeus, 1763) in southeastern Brazil. Shells from four species of bivalves were associated with the crabs: Eucallista purpurata (Lamarck, 1818), Chionopsis crenata (Gmelin, 1791), and Tivela zonaria (Lamarck, 1818) (Veneridae), and, most frequently (50%), Dallocardia delicatula (E.A. Smith, 1915) (Cardiidae). This was the first documented record of shellback crabs using valves of veneriid bivalves, as well as the first report of a crab-shell association for Hypoconcha in the South Atlantic Ocean. The relationship between the increase in size of shellback crabs and the size of the chosen shell was discussed.