Finless porpoises are named for and distinguished by the absence of a dorsal fin. Instead of this fin, there is a small ridge on their backs that starts just behind their blowhole and extends as far as the tail flukes. Small circular bumps called tubercles cover the ridge. They have unfused neck vertebrae, which enables unrestricted head movement, and they have a small, curving mouth. About half of them have pink eyes. Their streamlined body is blue-gray, though in northern China and Japan adults are light gray.