Portrait of a Reaper Cuttlefish (Sepia mestus)
A Gloomy Octopus (Octopus tetricus)
An Australian Giant Cuttlefish (Sepia apama) with Australian Mado (Atypichthys strigatus) on a rocky reef
A cephalopod is any member of the molluscan class Cephalopoda (Greek plural κεφαλόποδα (kephalópoda); "head-feet"). These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles (muscular hydrostats) modified from the primitive molluscan foot. Fishermen sometimes call them inkfish, referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology.