Cetaceans are 1 to more than 30 meters long, with a fish-like body shape, bare skin, only the muzzle with a few hairs, and no sweat glands or sebaceous glands. The front limbs are flippers, the hind limbs are completely degraded, and there is only one pair of small bone fragments in the body. The skin at the end of the tail extends from side to side to form a horizontal caudal fin. There is no auricle, because there is a thick layer of fat under the skin, through which the insulation and reduce the body weight, which is conducive to swimming. Some species have a dorsal fin.

Eyes are small, without transient membranes or lacrimal glands, and vision is poor. The external nostrils, 1 or 2, are located on the top of the head and are commonly known as blowholes. There are no auricles, but hearing is acute. Lungs 1 lobe on each side. Nursing in water. Stomach divided into 4 chambers. Usually lives 20 to 90 years in natural environment.

Extended information:

Whales rely mainly on echolocation to find food and avoid enemies. They generally feed on mollusks, fish and zooplankton, and some species can also prey on seals and fur seals. Every so often, they must change their breath.

In the whale's eyes, there is a gland that can secrete a kind of blubber tears, these "tears" to the salt seawater isolation, so that they are not like the eyes of other mammals, long-term immersion in seawater will have a sense of pain, which is a cetacean living in the ocean for a long time in a kind of adaptation.