* Whales and dolphins: These are mammals that breathe air through lungs.
* Sea turtles: These reptiles also breathe air through lungs.
* Sea snakes: Like other snakes, these reptiles breathe air through lungs.
* Manatees and dugongs: These are marine mammals that breathe air through lungs.
* Sea otters: These are mammals that breathe air through lungs.
* Polar bears: While not strictly water-dwelling, polar bears spend a lot of time in and around water and are excellent swimmers, using their lungs to breathe.
The key point is that these animals are vertebrates (animals with backbones), and while they live in water, they all breathe air through lungs.