An order of marine mammals comprising the whales, dolphins, and porpoises; it includes what is probably the largest known animal—the blue whale (Balaenoptera musculus), over 30 m long and over 150 tonnes in weight. The forelimbs of whales are modified as short stabilizing flippers and the skin is very thin and almost hairless. A thick layer of blubber insulates the body against heat loss and is an important food store. Whales breathe through a dorsal blowhole, which is closed when the animal is submerged. The toothed whales (suborder Odontoceti), such as the dolphins and killer whale, are carnivorous; whalebone whales (suborder Mysticeti), such as the blue whale, feed on plankton filtered by whalebone plates. Molecular systematics now indicates that whales are closely related to cows, camels, deer, and other members of the order Artiodactyla; hence they are classified with them in the superorder Cetartiodactyla.

http://uk.whales.org/ Website for the Whale and Dolphin Conservation Society