Ancient Greek: κῆτος,
lit. 'huge fish', sea monster) are
aquatic mammals constituting the
Cetacea (). Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel themselves through the water with powerful up-and-down movement of their tail which ends in a paddle-like fluke, using their flipper-shaped forelimbs to maneuver.
While the majority of Cetaceans live in marine environments, a small number exclusively reside in
brackish water or freshwater. Having a
cosmopolitan distribution, they can be found in some rivers and all of earth's oceans and many species inhabit vast ranges where they migrate with the changing of the seasons.
Cetaceans are famous for their high intelligence and complex social behaviour as well as the enormous size of some of its members, like the blue whale reaching a maximum confirmed length of 29.9 meters (98 feet) and weight of 173 tonnes (190 short tons), making it the largest animal known to have ever existed.
There are approximately 86 living species split into two
Odontoceti or toothed whales (containing
dolphins, other predatory whales like the
beluga and the
sperm whale, and the poorly understood
beaked whales) and the filter feeding
baleen whales (which includes species like the
blue whale, the
humpback whale and the
bowhead whale). (