|common Eastern (US) turtle|
The turtle's shell does more than keep the turtle safe; it also is a chemistry factory. When a turtle hibernates, it buries itself in cold water for up to five months. To survive, it has to change a lot of things about the way its body works. Some processes, such as fat burning, go anaerobic, without oxygen, when a turtle hibernates.
Turtles breathe in three main ways:
1. Through their lungs which is the primary means. This is why sea turtles can drown if they don't come up for air. But because of their shell, which is like a fused rib cage, they can't take in a deep breath, expanding their body cavity and lungs. Without ribs that expand and contract, the turtle's mouth breathing system is not like mammals. Instead, it has muscles that pull the body outwards towards the openings of the shell which allows it to inhale and muscles to squish the turtle's guts against its lungs to make it exhale. All of which uses a lot of energy.
2. Some species of aquatic turtles can absorb oxygen through their mouth and throat by taking in water both to smell and absorb oxygen.
3. In the butt breathers, sacs next to the cloaca expand. The walls of these sacs are lined with blood vessels and oxygen diffuses through the blood vessels. This process uses little energy. Usually they absorb less than 20 percent of their required oxygen this way. However, the Australian White-throated snapping turtle, aka the "bum-breathing turtle," can get nearly 70 percent of its oxygen through its cloaca.
Turtles aren't the only animals with interesting butts. Take the manatee, the large, somewhat comical, aquatic, mostly herbivorous marine mammals sometimes known as sea cows.