There are five main types of marine mammals.
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.
a mountain rising from the ocean seafloor that does not reach to the water's surface (sea level), and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from the seafloor to 1,000-4,000 meters (3,000-13,000 ft) in height. They are defined by oceanographers as independent features that rise to at least 1,000 metres (3,281 ft) above the seafloor. The peaks are often found hundreds to thousands of meters below the surface, and are therefore considered to be within the deep sea. There are an estimated 100,000 seamounts across the globe, with only a few having been studied. come in all shapes and sizes, and follow a distinctive pattern of growth, activity, and death. In recent years, several active seamounts have been observed, for example Loihi in the Hawaiian Islands. a fissure in a planet's surface from which geothermally heated water issues. are commonly found near volcanically active places, areas where tectonic plates are moving apart, ocean basins, and hotspots. exist because the earth is both geologically active and has large amounts of water on its surface and within its crust. Common land types include hot springs, fumaroles and geysers. Under the sea, they may form features called black smokers. Relative to the majority of the deep sea, the areas around submarine are biologically more productive, often hosting complex communities fueled by the chemicals dissolved in the vent fluids. Chemosynthetic archaea form the base of the food chain, supporting diverse organisms, including giant tube worms, clams, limpets and shrimp. Active hydrothermal vents are believed to exist on Jupiter's moon Europa, and ancient vents have been speculated to exist on Mars.