Every turtle needs air. Even the ones that seem to live in the water have lungs and must come up to breathe. So how do some of them stay underwater for weeks, or ride out a whole winter beneath a frozen pond?
The answer sounds like a joke, but it's true: some turtles can take in oxygen through their rear end. Scientists call it cloacal respiration. The cloaca is the single opening at a turtle's tail end, and in certain species it holds special sacs that soak up dissolved oxygen from the water. It doesn't replace the lungs, but it gives these turtles a remarkable backup supply.
How Breathing From Behind Works
Inside the cloaca of these turtles are large sacs lined with many tiny, finger-like projections. All those little folds create lots of surface area. As water flows in and out, oxygen dissolved in it passes into the turtle's blood, a bit like how a fish's gills work.
This trick is most important for turtles that specialize in diving. Some rely on it heavily while they're underwater, using a pair of extra bladders connected to the cloaca to absorb oxygen from the surrounding water.
The Champion: Australia's 'Bum-Breathing Turtle'
The star of this story lives in Queensland, Australia. The Fitzroy River turtle is so good at this that it's commonly known as the 'bum-breathing turtle.' It can get up to 70 percent of its oxygen needs from the water through its cloaca.
That ability lets it stay underwater for up to three weeks. Its cloaca contains two enlarged sacs lined with branching projections that pull oxygen from the river. Sadly, the species is listed as vulnerable. Dams, farming, and muddy water can lower the oxygen in its rivers, which makes its unusual way of breathing harder.
Closer to Home: The Painted Turtle
You don't need to travel to Australia to find a turtle with this talent. The painted turtle, a familiar sight sunning itself on logs across much of North America, can breathe through its cloaca too. It also has special skin cells that absorb oxygen from the water, which scientists call cutaneous respiration.
These tricks help painted turtles survive cold winters. When ponds freeze over, the turtles become locked beneath the ice, often in water with little or no oxygen. They essentially hold their breath until spring. They slow their bodies way down, live off energy stored in the liver, and even use their shells to help neutralize the acid that builds up when the body runs without oxygen.
That makes the painted turtle one of the best-studied backboned animals that can survive long periods without oxygen. Not bad for a little pond turtle.
Lungs Inside a Box
Turtles have another breathing challenge most animals don't. Their rigid shell can't expand, so their chest can't swell up to fill the lungs the way ours does. Instead, the lungs are attached right to the top of the shell.
To breathe, turtles use groups of muscles that push and pull on their internal organs. Their large liver presses against the lungs to push air out, then is pulled back down so air can flow back in. It's a bit like squeezing and releasing a bellows from the inside.
Turtles aren't the only ones with an unusual backup plan. Sea cucumbers draw water in through the anus to collect oxygen, and the pond loach, a small fish, can exchange gases through the end of its gut while buried in mud during dry spells.
So the next time you see a turtle sitting quietly at the bottom of a pond, remember it may be doing something you'd never guess. Nature found a clever answer to staying underwater, even if it came from a surprising direction.
