Marine biology gannets, and auks. Although they spend most of their lives in the ocean, species such as gulls can often be found thousands of miles inland. There are five main types of marine mammals, namely cetaceans (toothed whales and baleen whales); sirenians such as manatees; pinnipeds including seals and the walrus; sea otters; and the polar bear. All are air-breathing, and while some such as the sperm whale can dive for prolonged periods, all must return to the surface to breathe. Marine habitats can be divided into coastal and open ocean habitats. Coastal habitats are found in the area that extends
Toothed whale Some species log out of the water, which may allow then to travel faster. Their skeletal anatomy allows them to be fast swimmers. Most species have a dorsal fin. Most toothed whales are adapted for diving to great depths, porpoises are one exception. In addition to their streamlined bodies, they can slow their heart rate to conserve oxygen; blood is rerouted from tissue tolerant of water pressure to the heart and brain among other organs; haemoglobin and myoglobin store oxygen in body tissue; and they have twice the concentration of myoglobin than haemoglobin. Before going on long dives, many toothed