Mammals nurse their young with milk. Mammals have hair, at least at some stage in their development. The scientific order Cetacea includes all whales. The word Mysticeti is derived from the Greek word for moustache, mystax. It may refer to the hairy appearance of the baleen plates, which baleen whales have instead of teeth.
Baleen whales have two external blowholes and are larger in size than most toothed whales.
Right whales have no dorsal fin, no throat grooves, and extremely long baleen plates contained in a hugely arched jaw. This family has one living member, the gray whale. The gray whale has a few throat grooves, short baleen plates, and a small dorsal hump followed by a series of bumps. Some scientists recognize a fourth family, Neobalaenidae, which contains the pygmy right whale. Unlike other members of the right whale family, the pygmy right whale has a dorsal fin.