ORDER CETACEA: Whales & dolphins

Marine creatures that look more like fish than other mammals. They lack arms and legs, have flukes and fishlike tails, and no visible body hair. In fact, whales have hair near the blowhole, and a few other places when young. Like other mammals, whales breath through a nostril (the blowhole) and via lungs, not gills. The body is insulated with a thick layer of fat called blubber, which allows them to retain body heat in Arctic and deep waters. 

Whales navigate by means of a complex sonar system, with sounds analyzed by a structure in the head called the melon. The sounds produced vary enormously. Some are used for navigation, while others seem to be "songs" to communicate with other whales. The sounds may be heard many hundreds of mile away from the singer.

Whales fall into two large groups. The first contains toothed whales, which have teeth in the lower jaws and tend to feed on other vertebrates. Included are the sperm whale, orca, and dolphins. The second group has specialized teeth that form long thin strainers called baleen, and they feed on small organisms such as krill and plankton. To this group are the largest living animals, including blue, humpback and right whales.