Pinnipeds  are the seals and their relatives, a group of semi-aquatic marine mammals. The Pinnipedia is in the Order Carnivora. 
There are three seal families: Odobenidae (walruses), Otariidae (eared seals, including sea lions and fur seals), and Phocidae (true seals). 

Seals are sleek-bodied and barrel-shaped. Their bodies are well adapted to the aquatic habitat where they spend most of their lives. Pinnipeds have flippers for hands, big bulky bodies, doggish faces, and big eyes. Unlike cetaceans, pinnipeds have their noses on their faces, and each nostril of the nose closes when the pinniped goes underwater. Like cetaceans, pinnipeds have a thick layer of blubber (fat) just under their skin: this blubber keeps them warm in cold waters and keeps them fed during times when food is not easily found. When they cannot find food, they live off the fat in the blubber.

Pinnipeds are carnivorous. This means they eat only meat (such as fish or squid) and not plants. However, almost all pinnipeds can be eaten by polar bears, sharks and killer whales.

Seals are often trained in zoos or aquariums to put on shows. However, in Sweden, it is illegal to train a seal to balance a ball on its nose.

Sleep 
Pinnipeds sleep in the water. They may also sleep on land. In both environments, there is a danger. At least in the northern hemisphere, there is danger from polar bears on land, and in the water, there is danger from sharks. While sleeping in water, the animals go through different stages of sleep. They do some behaviors during sleep: they come to the surface occasionally to breathe, and they now and then open an eye for a period of time. The details vary in different species or groups. Similar adaptations are found in cetaceans like dolphins.

Taxonomy 
 Family Phocidae (Earless seals or true seals)
 Subfamily Monachinae
 Tribe Monachini
 Genus Monachus
 Tribe Mirungaini
 Genus Mirounga: Elephant seals
 Tribe Lobodontini
 Genus Ommatophoca
 Ross seal (Ommatophoca rossii)
 Genus Lobodon
 Crabeater seal (Lobodon carcinophagus)
 Genus Hydrurga
 Leopard seal (Hydrurga leptonyx)
 Genus Leptonychotes
 Weddell seal (Leptonychotes weddellii)
 Subfamily Phocinae
 (placed here)
 Genus Cystophora
 Hooded seal (Cystophora cristata)
 Genus Erignathus
 Bearded seal (Erignathus barbatus)
 Tribe Phocini
 Genus Histriophoca 
Ribbon seal (Histriophoca fasciata)
 Genus Phoca
 Spotted seal (Phoca largha)
 Common seal or Harbor Seal (Phoca vitulina)
 Harp seal (Phoca groenlandica, formerly Pagophilus groenlandicus)
 Genus Pusa
 Ringed seal (Pusa hispida, formerly Phoca hispida)
 Caspian seal (Pusa caspica, formerly Phoca caspica)
 Baikal seal or Nerpa (Pusa sibirica, formerly Phoca sibirica)
 Genus Halichoerus
 Grey seal (Halichoerus grypus)

 Family Otariidae (Eared seals)
 Genus Arctocephalus (Fur seals)
 Antarctic fur seal (Arctocephalus gazella)
 Brown fur seal (Arctocephalus pusillus)
 Genus Callorhinus
 Northern fur seal (Callorhinus ursinus)
 Genus Eumetopias
 Steller sea lion or Northern Sea Lion (Eumetopias jubatus)
 Genus Neophoca
 Australian sea lion (Neophoca cinerea) 
 Genus Otaria
 South American sea lion or Southern Sea Lion (Otaria flavescens, formerly Otaria byronia) 
 Genus Phocarctos
 New Zealand sea lion (Phocarctos hookeri)
 Genus Zalophus
 California sea lion (Zalophus californianus)

 Family Odobenidae (Walruses)
 Walrus (Odobenus rosmarus)

References 

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