The Order Cetacea
Cetaceans, the mammals most completely adapted to life in the water, have streamlined bodies tapering towards the tail. They cannot move about on land, their skin needs moisture continuously and, since they have no breastbone, most of them die if stranded on land because of the pressure on their lungs. Whales have no hind limbs. Their forelimbs are modified into broad flippers, and the tail has a horizontal fluke projecting on each side. A layer of blubber covers the whole body beneath the skin and helps to conserve heat. There are no external ears. The horizontal tail immediately distinguishes whales from fish.
Sub-Order Odontoceti
Generally much smaller than the whalebone whales, toothed whales have conical, pointed teeth in the lower or both jaws, or only one tusk-like tooth in the upper jaw. The lower jaw is narrow, not bowed outwards as in the baleen whales, and the tongue is small. Toothed whales feed mainly on fish.

Killer whale image
Family Platanistidae
River dolphins: 4 species
All freshwater dolphins have long, almost bird-like beaks which may contain as many as 200 teeth. They live in the Amazon, Orinoco, Yangtse and Ganges rivers.
River dolphin image
Family Ziphiidae
Beaked whales: 15 species
These medium-sized whales have a beak, one or two pairs of functional teeth in the lower jaw, and two to four throat furrows converging to form a V-pattern at the chin.
Beaked whale image
Family Physeteridae
Sperm whales: 2 species
These whales have no dorsal fin and have functional teeth in the lower jaw, which is much shorter than the upper. The larger species has a barrel-shaped head, which is a third of the total body length and is filled with spermaceti oil, used in industry as a lubricant. It feeds mainly on squids. The pygmy sperm whale has a porpoise-like body.
Sperm whale image
Family Monodontidae
White whales: 2 species
White whales are closely related to the dolphins but have fewer teeth and no dorsal fin. The species are the beluga (or white) whale and the narwhal.

Beluga image
Family Delphinidae
Dolphins and porpoises: 50 species
These mammals, generally small compared with other whales, have no throat grooves, they have teeth in both jaws, and most have a dorsal fin in the centre of the back.

avi, 1 MB

Dolphin image

Sub-Order Mysticeti
Most species of whalebone whales are large - there is none less than 17ft long when fully grown. There are no teeth in either jaw; instead the V-shaped upper jaw has plates of baleen (whalebone), which act as sieves or strainers for plankton and are enclosed by the two halves of the lower jaw when the whale is not feeding.
Humpback whale image
Family Eschrichtiidae
There is one species: the Californian grey whale Eschrichtius gibbosus. This whale migrates from Arctic waters to shallows off the Californian coast to breed. It has a very broad mouth, 2-4ft deep furrows on the throat, and no dorsal fin but a series of low bumps on the back near the tail. The baleen is short and thick with coarsely frayed inner edges to strain the small bottom-living creatures on which this whale feeds.
Grey whale tale image
Family Balaenopteridae
Rorquals: 6 species
Also called fin whales, the rorquals are distinguished from the right whales by a dorsal fin, narrow ridges on the throat, a smaller head (generally a quarter or a fifth of the body length), only slightly curved jaws, and shorter and less flexible baleen.

Blue whale image
Family Balaenidae
Right whales: 3 species
These whales have long mouths - the head is more than a quarter of the total body length - and the lower jaw scoops down at the front so that it encloses the upper jaw only at the sides. There are no throat grooves and no dorsal fin. The baleen plates are long, narrow and very elastic, and these whales feed only on miscroscopic plankton.
Right Whale image

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