Science, Tech, Math › Animals & Nature Types of Marine Mammals Share Flipboard Email Print Animals & Nature Marine Life Marine Life Profiles Marine Habitat Profiles Sharks Key Terms Amphibians Birds Habitat Profiles Mammals Reptiles Wildlife Conservation Insects Forestry Dinosaurs Evolution View More By Jennifer Kennedy Marine Science Expert M.S., Resource Administration and Management, University of New Hampshire B.S., Natural Resources, Cornell University Jennifer Kennedy, M.S., is an environmental educator specializing in marine life. She serves as the executive director of the Blue Ocean Society for Marine Conservation. our editorial process Jennifer Kennedy Updated February 04, 2019 Marine mammals are a fascinating group of animals, and come in a wide variety of sizes and shapes, from the sleek, streamlined, water-dependent dolphins to the furry seals that haul out on the rocky coast. Learn more about the types of marine mammals below. 01 of 05 Cetaceans (Whales, Dolphins and Porpoises) Cultura / Richard Robinson / Cultura Exclusive / Getty Images Cetaceans differ greatly in their appearance, distribution, and behavior. The word cetacean is used to describe all whales, dolphins and porpoises in the order Cetacea. This word comes from the Latin cetus meaning "a large sea animal," and the Greek word ketos, meaning "sea monster." There are about 86 species of cetaceans. The term "about" is used because as scientists learn more about these fascinating animals, new species are discovered or populations are re-classified. Cetaceans range in size from the tiniest dolphin, Hector's dolphin, which is just over 39 inches long, to the largest whale, the blue whale, which can be over 100 feet long. Cetaceans live in all of the oceans and many of the major rivers of the world. 02 of 05 Pinnipeds Alastair Pollock Photography / Moment / Getty Images The word "pinniped" is Latin for wing- or fin-footed. Pinnipeds are found all over the world. The pinnipeds are in the order Carnivora and suborder Pinnipedia, which includes all the seals, sea lions, and the walrus. There are three families of pinnipeds: the Phocidae, the earless or ‘true’ seals; the Otariidae, the eared seals, and the Odobenidae, the walrus. These three families contain 33 species, all of whom are well-adapted for a life spent on both land and in the water. 03 of 05 Sirenians Borut Furlan / WaterFrame / Getty Images Sirenians are animals in the Order Sirenia, which includes manatees and dugongs, also known as "sea cows," probably because they graze on sea grasses and other aquatic plants. This order also contains the Steller's sea cow, which is now extinct. The sirenians that remain are found along the coasts and inland waterways of the United States, Central and South America, West Africa, Asia, and Australia. 04 of 05 Mustelids heatherwest / Getty Images The mustelids are the group of mammals that include weasels, martens, otters, and badgers. Two species in this group are found in marine habitats - the sea otter (Enhydra lutris), which lives in Pacific coastal areas from Alaska to California, and in Russia, and the sea cat, or marine otter (Lontra felina), which lives along the Pacific coast of South America. 05 of 05 Polar Bears Mint Images / Frans Lanting / Getty Images Polar bears have webbed feet, are excellent swimmers, and prey primarily upon seals. They live in Arctic regions and are threatened by decreasing sea ice. Did you know that polar bears have clear fur? Each of their hairs is hollow, so they reflect light, giving the bear a white appearance.