Octopuses are marine mollusks in the class Cephalopoda. The cephalopods, whose name literally means head foot, have their appendages attached to the head and include octopuses, squids, and nautiluses. The octopuses (order Octopoda) have only eight appendages or arms, and unlike other cephalopods, they lack shells, pens, and tentacles. There are two groups of Octopoda, the cirrate and the incirrate. The cirrate have cirri (cilia-like strands on the suckers),possess paddle-shaped fins suitable for swimming in their deep ocean pelagic and epibenthic habitats (Boyle and Rodhouse 2005), and are much less common than the incirrate which contain the more traditional forms of octopus. Octopuses are found in every ocean in the world and range in size from less than 20 cm (total length) to over 3 m (total length); the latter is a record held by Enteroctopus dofleini (Wülker 1910). E. dofleini is one of at least eight species of octopus (Table 22.1) found in the Bering Sea, including one newly identified species. Members of these nine species represent seven genera and can be found from less than 10-m to greater than 1500-m depth. All but one, Japetella diaphana are benthic octopuses. The mesopelagic Vampyroteuthis infernalis is a cephalopod that shares similarities with both octopuses and squids. But is included in the octopus assessment. The state of knowledge of octopuses in the BSAI, including the true species composition, is very limited.
