Porpoises are marine mammals with streamlined bodies adapted for swimming. They have a rounded snout, a robust torso, and a dorsal fin that helps with stability. Their skin is smooth and often dark gray or blue, which aids in camouflage against predators. Porpoises possess a layer of blubber for insulation in cold waters. Their anatomy includes a set of sharp teeth, which they use to catch fish and squid. Porpoises have a complex respiratory system, featuring a blowhole on top of their heads for breathing. They also have excellent hearing, which is crucial for communication and navigation in their underwater environment.