Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises,which belong to suborder Odontoceti (toothed whales). This suborder also includes the sperm whale, killer whale, pilot whale, and beluga whale. The other Cetacean suborder Mysticeti (baleen whales), are filter feeders that eat small organisms caught by straining seawater through a comblike structure found in the mouth called baleen. This suborder includes the blue whale, the humpback whale, the bowhead whale and the minke whale. All Cetacea have forelimbs modified as fins, a tail with horizontal flukes, and nasal openings (blowholes) on top of the head.
Whales range in size from the blue whale, the largest animal known to have ever existed at 35 m (115 ft) and 136 tonnes (134 long tons; 150 short tons), to various pygmy species, such as the pygmy sperm whale at 3.5 m (11 ft).
Whales collectively inhabit all the world's oceans and number in the millions, with annual population growth rate estimates for various species ranging from 3-13%. For centuries, whales have been hunted for meat and as a source of raw materials. By the middle of the 20th century, however, industrial whaling had left many species seriously endangered, leading to the end of whaling in all but a few countries.
Like all mammals, whales breathe air, are warm-blooded, nurse their young with milk from mammary glands, and have body hair. Beneath the skin lies a layer of fat called blubber, which stores energy and insulates the body. Whales have a spinal column, a vestigial pelvic bone, and a four-chambered heart. The neck vertebrae are typically fused, trading flexibility for stability during swimming.