Sea snake
All snakes are good swimmers, but only real sea snakes live their whole lives in the ocean. Not only do they live there, they eat there and even have their young right inside the water. Most cannot live at all on land. If they get forced onto land by a storm or powerful currents, they are unable to move. Sea snakes have no scutes (special scales on snakes' bellies that help them grip and slither across the ground), so if a sea snake ends up on a beach, it is unable to slither back out to sea. Instead, sea snakes have a paddle-shaped tail. With its tail, the snake can swim well.