Marine mammals are mammals who live in and feed off the ocean. But they are like any other mammals, warm blooded. They have lungs and they breathe. They give birth to living kids who depends on milk from their mothers until they are grown enough to hunt their own food.

Marine Mammals
Facts about sea mammals
There are considered to be three main groups of marine mammals: whales, seals and sea cows. Whales and sea cows are placed in their own orders: Catacea and Sirenia. The seals are called Pinnipedia. This is a subgroup of the carnivore order (Carnivora), which also includes all land carnivores.