any of several marine cephalopods of the order Sepioidea, related to the octopus and squid and characterized by a thick, internal, calcified shell called the cuttlebone. The approximately 100 species of cuttlefish range between 2.5 and 90 centimetres (1 to 35 inches) and have somewhat flattened bodies bordered by a pair of narrow fins. All species have eight arms and two longer tentacles that are used in capturing prey and can be withdrawn into two pouches. Suction disks are located on the arms and on expanded pads at the tips of the tentacles.