colossal squid

The colossal squid (Mesonychoteuthis hamiltoni) is the largest member of its family Cranchiidae, the cockatoo or glass squids, with its second largest member being Megalocranchia fisheri. It is sometimes called the Antarctic cranch squid or giant squid (not to be mistaken for the giant squid known as architeuthis) and is believed to be the largest squid species in terms of mass. It is the only recognized member of the genus Mesonychoteuthis and is known from only a small number of specimens. The species is confirmed to reach a mass of at least , though the largest specimens—known only from beaks found in sperm whale stomachs—may perhaps weigh as much as , making it the largest known invertebrate. Maximum total length has been estimated at . The colossal squid has the largest eyes of any known creature ever to exist, with an estimated diameter of 27 cm (11 in). The species has similar anatomy to other members of its family, although it is the only member of Cranchiidae to display hooks on its arms and tentacles. It is known to inhabit the circumantarctic Southern Ocean. Although little is known about the behaviour, it is known to use bioluminescence to attract prey. It is presumed to be an ambush predator, and is a major prey of the sperm whale. The first specimens were discovered and described in 1925. In 1981, an adult specimen was discovered, and in 2003 a second specimen was collected. Captured in 2007, the largest colossal squid weighed , and is now on display at the Museum of New Zealand Te Papa Tongarewa. Morphology The colossal squid shares features common to all squids: a mantle for locomotion, one pair of gills, a beak or tooth, and certain external characteristics like eight arms and two tentacles, a head, and two fins. In general, the morphology and anatomy of the colossal squid are the same as any other squid. However, there are certain morphological characteristics that separate the colossal squid from other squids in its family: the colossal squid is the only squid in its family with hooks, either swivelling or three-pointed, equipped on its arms and tentacles. There are squids in other families that also have hooks, but no other squid in the family Cranchiidae.