Cranchiidae in the context of Open ocean

The colossal squid (Mesonychoteuthis hamiltoni) is a species of very large squid belonging to the family Cranchiidae, that of the cockatoo squids or glass squids. It is sometimes called the Antarctic cranch squid or giant squid (not to be confused with the giant squid in genus Architeuthis) and is believed to be the largest squid species in terms of mass. It is the only recognized member of the genus Mesonychoteuthis.

The species is confirmed to reach a mass of at least 495 kilograms (1,091 lb), though the largest specimens—known only from beaks found in sperm whale stomachs—may perhaps weigh as much as 600–700 kilograms (1,300–1,500 lb), making it the largest extant invertebrate. Maximum total length is ~4.2 metres (14 ft). Larger estimates exist, however these include the feeding tentacles measured on dead specimens; in life the squid's tentacles are hidden, only released when capturing prey. If tentacles are considered, lengths of 10 metres (33 ft) and 14 metres (46 ft) exist, but the former estimate is more likely. The colossal squid has the largest eyes of any known creature ever to exist, with an estimated diameter of 27–30 cm (11–12 in) to 40 cm (16 in) for the largest collected specimen.