Cetaceans include toothed whales (Suborder Odontoceti),such as the Sperm Whale,dolphins,and porpoises such as the Dall's porpoise.Cetaceans also include baleen whales (Suborder Mysticeti),such as the Gray Whale,Humpback Whale,and Blue Whale.
Sirenians include manatees,the Dugong,and the extinct Steller's Sea Cow.
Seals (Family Phocidae),sea lions (Family Otariidae - which also include the fur seals),and the Walrus (Family Odobenidae) are all considered pinnipeds.
The Sea Otter is a member of the Family Mustelidae,which includes weasels and badgers.
The Polar Bear (Family Ursidae) is sometimes considered a marine mammal because of its dependence on the sea.
