Sea snakes have special nostrils that can close when they go underwater and open when they come up to breathe, like the blowhole of a whale (scientists call these "valved" nostrils). The nostrils are found high up on the head so that the entire snake can stay under the water when they come up to breathe. In its search for food, a sea snake may remain under water for a long time. To do this, sea snakes have evolved a single lung that almost is as long as the whole body.