Portunidae

Portunidae is a family of crabs which contains the swimming crabs. Portunid crabs are characterised by the flattening of the fifth pair of legs into broad paddles, which are used for swimming. This ability, together with their strong, sharp claws, allows many species to be fast and aggressive predators. Its members include many well-known shoreline crabs, such as the European shore crab (Carcinus maenas), blue crab (Callinectes sapidus), velvet crab (Necora puber) and lady crab (Ovalipes ocellatus). Two genera in the family are contrastingly named Scylla and Charybdis; the former contains the economically important species black crab (Scylla serrata) and Scylla paramamosain. The circumscription of the family varies, with some authors treating 'Carcinidae', 'Catoptridae' and 'Macropipidae' as separate families, and others considering them subfamilies of a wider Portunidae. Swimming crabs reach their greatest species diversity in the Pacific and Indian Oceans. Extinct genera are marked with an obelisk.