cetacea

‖n. pl. [ NL., from L. cetus whale, Gr. &unr_;. ] (Zool.) An order of marine mammals, including the whales. Like ordinary mammals they breathe by means of lungs, and bring forth living young which they suckle for some time. The anterior limbs are changed to paddles; the tail flukes are horizontal. There are two living suborders: (a) The Mysticete or whalebone whales, having no true teeth after birth, but with a series of plates of whalebone [ see Baleen. ] hanging down from the upper jaw on each side, thus making a strainer, through which they receive the small animals upon which they feed. (b) The Denticete, including the dolphins and sperm whale, which have teeth. Another suborder (Zeuglodontia) is extinct. The Sirenia were formerly included in the Cetacea, but are now made a separate order. [ 1913 Webster ]