NARWHAL, a cetacean (Monodon monoceros), character ized by the presence in the male of a long horn-like tusk. In the adult of both sexes there are only two teeth, both in the upper jaw, which lie horizontally side by side, and in the female remain throughout life concealed in cavities of the bone. In the male the right tooth usually remains similarly concealed, but the left is immensely developed, attaining a length equal to nearly that of the entire animal. It projects forwards from the head in the form of a cylindrical or slightly tapering, pointed tusk, composed of ivory, with a central cavity reaching almost to the apex, with out enamel, and with the surface marked by grooves and ridges running in a left-handed spiral. Occasionally both left and right tusks are developed. In young animals several small additional teeth are present, but these generally disappear soon after birth.
The head is short and rounded ; the fore limbs or paddles are small and broad, and (as in the Beluga) a dorsal fin is wanting.
The general colour is dark grey variously marbled and spotted with grey.
The narwhal is an Arctic whale rarely seen south of 65° N. lat. Like most cetaceans it is gregarious and usually met with in "schools" of 15 or 20 individuals. Its food appears to be cuttlefishes, small fishes and crustaceans. The purpose served by the tusk is uncertain. The narwhal is extremely playful, indi viduals frequently elevating their tusks and crossing them with each other as in fencing. They have never been known to charge and pierce the bottom of ships with their weapons as the sword fish does. The ivory of the tusk is of good quality, but owing to the central cavity, only fitted for the manufacture of objects of small size. The entire tusks are sometimes used for decorative purposes. (See CETACEA.)