The Colossal Squid (Mesonychoteuthis hamiltoni), sometimes called the Antarctic squid or giant cranch squid, is a species of squid that can only be found in extremely deep oceans. 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 500 kilograms (1,100 pounds), 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 pounds), making it the largest-known invertebrate. Maximum total length has been estimated at 9–10 meters (30–33 feet).
Unlike the giant squid, who has only suckers lined with small teeth in all of their arms and tentacles, the colossal squid's limbs are also equipped with suckers lined with small teeth and sharp hooks: some swiveling, others 3-pointed. Its body is wider and stouter, and therefore heavier, than that of the giant squid. Colossal squid are believed to have longer mantles than the giant squid, but shorter tentacles.
The colossal squid exhibits abyssal gigantism. The beak of the colossal is the largest known of any squid, and more robust than that of the giant squid. The colossal squid also has the largest eyes documented in the animal kingdom; a partly collapsed specimen measured 27 cm (11 in) in diameter, with a 9 centimeters (3.5 inches) pupil. The eye was estimated to be 30 to 40 centimeters (12 to 16 inches) when the squid was alive.
The colossal squid's known range extends thousands of kilometers north of Antarctica to southern South America, southern South Africa, and the southern tip of New Zealand, making it primarily an inhabitant of the entire circumantarctic Southern Ocean. Their eyes also glow in the dark.