Mammals inhabiting the sea; generally taken to include the cetaceans (whales, porpoise, dolphin), the sirenians (sea-cows, including manatees and dugong) and the pinnipeds (the carnivores of the group, seals, sealions, walruses). Other mammals that spend a great deal of time in the water but are not classified as marine mammals are the polar bear and the sea otter.




