There are two major groups of whales—the toothed whales (suborder Odontoceti) and the toothless baleen whales (suborder Mysticeti).Toothed Whales
Toothed whales include two families that are widely distributed, the beaked and bottlenose whales (family Ziphiidae) and the sperm whale, or cachalot (family Physeteridae; DNA studies suggest, however, that it is more closely related to baleen whales); the beluga, or white whale, and the narwhal (family Monodontidae), small polar whales with no dorsal fin and only a few teeth; the river dolphins (family Platanispidae), which inhabit muddy rivers of India and South America; and several families better known as ocean dolphins and porpoises. The killer whale and pilot whale are types of dolphin. The white whale Moby-Dick, of Herman Melville's novel, was not a beluga but a sperm whale with prominent white features.
Toothed whales range in length from 4 to 60 ft (1.3–18.5 m). They catch fast-moving prey, like fish or squid. Many species use echolocation (sonar) for underwater navigation and hunting. They have a single blowhole and a wide throat to accommodate large prey. Some of the larger ones, like the sperm whale, can dive as deep as 1 mi (1.6 km).
There are three families of baleen whales: the right whale family (Balaenidae), including the bowhead, or Greenland whale; the gray whale family (Eschrichtidae), with a single species ( Eschrichtius robustus ) found in the N Pacific Ocean; and the rorqual family (Balaenopteridae). Rorquals, the most familiar of the large whales, have large, pouchlike throats with furrows running from mouth to belly. The family includes the humpback whale, the sei whale, the minke whale, the Bryde's whale, the fin whale (or common rorqual), and the blue whale, which can grow to a length of 100 ft (30 m) and a weight of 150 tons.
Baleen whales are large species, usually over 33 ft (10 m) long. They are filter feeders, living on shrimplike krill, plankton, and small fish. They lack teeth but have brushlike sheets of a horny material called baleen, or whalebone, edging the roof of the mouth. With these strainers and their enormous tongues, tons of food can be separated from seawater. Baleen whales have narrow throats and paired blowholes. Male humpbacks produce a repeated pattern of sounds called a song during the mating season; the purpose is not clear, as all males in a group sing basically the same song.