right whale, name for whales of the family Balaenidae. They were so named by whalers, who for centuries considered them "the right whales" to hunt, because they float when killed and because they yield enormous quantities of oil and of baleen. Baleen, or whalebone, is the substance forming the fringed, triangular plates that hang from the roof of the whale's mouth and serve as a filter for plankton. It commanded such a high price in the 19th cent. that baleen whales (right whales and rorquals) were nearly exterminated by hunting. Right whales are distinguished from rorquals by the lack both of a dorsal fin and of neck furrows. Their girth is great in proportion to their length, and they have two thick pectoral fins. The lower jaws are scooplike in shape; the upper jaws contain about 300 baleen plates.
The black right whale ( Eubalaena glacialis ) is usually black all over; some individuals have white undersides. The female, larger than the male, averages 45 to 60 ft (14–18 m) in length. There is an irregularly shaped, horny growth, called the bonnet, above the snout. It has no known function, other than possible intraspecific aggression, and accumulates an immense conglomeration of parasites. There are three subspecies of black right whales, inhabiting the N Atlantic and N Pacific oceans and the Southern Hemisphere, respectively. The northern populations travel to the equator in winter, breeding on their way back to the poles. The bowhead, Greenland, or Arctic right whale ( Balaena mysticetus ) remains near the ice front all year, following its seasonal advances and recessions. It is black with a white chin and often a white tail band; there is a bump on top of the head. Its baleen plates grow up to 13 ft (4 m) long, and it produces large quantities of oil. The 20-foot-long (6-m) pygmy right whale ( Caperea marginata ) is found in the waters of Australia and New Zealand. (Some authorities place it in a separate family, Neobalaenidae.) All three species are rare and endangered. Right whales are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Cetacea, family Balaenidae.