narwhal (närˈwəl) [key], a small arctic whale, Monodon monoceros. The males of this species, and an occasional female, bear a single, tightly spiraled tusk that measures up to 9 ft (2.7 m) in length. This tusk is an overgrown upper central incisor tooth, generally the one on the left. Very rarely do both incisors grow out in this manner; the animal is otherwise toothless. The tusk is nerve-rich and may be used as a sense organ and for other functions. The narwhal is short-headed and virtually snoutless. When mature, it is mottled gray in color. Like its close relative the beluga, it lacks a dorsal fin, but it does have a long, low dorsal hump. The narwhal may reach a length of 20 ft (6.1 m), excluding the tusk. It is found in the Arctic and N Atlantic oceans, occasionally as far south as Britain; narwhals usually travel in groups of 15 to 20 animals. The diet of narwhals consists chiefly of cuttlefish and cod. Mating occurs in the summer, and after a gestation of 14 months the female gives birth to a single blue-gray calf measuring up to 5 ft (1.5 m). The calves are weaned at six months. Formerly killed for its tusk, which was believed to have magical properties (and was sold for centuries as a unicorn horn), the narwhal is now hunted by native peoples for food and for the tusk. It is classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Cetacea, family Monodontidae.
See studies by F. Bruemmer (1993), J. Rosing (1999), and T. McLeish (2013).