Cetaceans, which include whales, dolphins, and porpoises, are marine mammals characterized by their streamlined bodies and adaptations for life in water. They possess a layer of blubber for insulation, a dorsal fin for stability, and flippers for steering. Their elongated skulls house blowholes on top, allowing them to breathe easily at the surface. Cetacean anatomy also features specialized adaptations for echolocation, particularly in dolphins and porpoises. They have a complex system of air sacs and a fatty organ called the melon, which helps focus sound waves. Their large brains are highly developed, supporting advanced social behaviors and communication.