Vertebrates

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Pinnipeds are carnivores that live both on land and in the water,  and use flippers to get around. They spend the majority of their lives in the water swimming and eating and only come onto land or ice to give birth, rest, or shed. Pinnipeds are separated into three groups: earless seals, eared seals, and walruses. Some examples are sea lions, seals, and walruses. 

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Cetaceans are categorized into 2 groups: baleen whales and toothed whales. There are 70 different species of cetaceans between the 2 groups. Cetaceans spend their lives in the water. Some examples being whales, dolphins, and porpoises. 

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Sirenians are herbivores who eat sea grass that grows in coastal waters. They spend their entire lives in the water residing in rivers, wetlands, swamps, and coastal marine waters. Sirenians are composed of 1 species of dugongs and 3 species of manatees, but the dugongs are the only sirenians that live in freshwater environments.

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Marine fissipeds, which means “split-footed”, are members of the order Carnivora and are more closely related to terrestrial carnivores than seals or whales despite being considered marine mammals. Two examples of marine fissipeds are polar bears and sea otters. Polar bears are native to the Arctic, and spend most of their lives on marine ice hunting various species of seals. However, sea otters spend most of their life in the water, staying insulated in the cold water through trapped air in their thick fur, with a diet that is primarily composed of marine invertebrates.