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Whale, one of the order Cetacea of large, wholly aquatic mammals. All are highly adapted for life in water, with a torpedo-shaped body, front limbs reduced and modified as steering paddles, and hind limbs absent. They have a tail of 2 transverse flukes and swim by up-and-down movements of this tail. Most species have a fleshy dorsal fin that acts as a stabilizer. The neck is short, the head flowing directly into the trunk. The body is hairless, and the smooth skin lies over a thick layer of blubber that has an insulating function but also acts to smooth out the passage of water over the body in rapid swimming. The nose, or blowhole, is at the top of the head, allowing the animal to breathe as soon as it breaks the surface of the water.

Modern whales divide into 2 suborders, the whalebone whales and the toothed whales. Whalebone whales feed on plankton, straining the enormous quantities they require from the water with special plates of whalebone, or baleen, developed from the mucus membrane of the upper jaw. Whalebone whales—the right, rorqual, and gray whales—are usually large and slow-moving. The group includes the blue whale (Balaenoptera musulus), the largest animal of all time (up to 100 ft/30.5 m long). Toothed whales, equipped with conical teeth, feed on fishes and squids. The group includes the dolphins and porpoises, the sperm whale (Physeter macrocephalus), and the narwhal (Mmonodon monoceros). Many species of whale are endangered.

See also: Whaling.

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