Elusor macrurus turtles live most of their lives underwater. On land, wild dogs, foxes, monitor lizards and other predators wait for them. All of them do not mind gorging themselves on turtle meat. The shells of water turtles are not as strong as those of land turtles. Therefore, they are often prey for predators – both terrestrial and aquatic.
So Elusor macrurus has learned to hide in the mud. But then how do they breathe? All turtles breathe through their nostrils. Even water turtles have to float to the surface to breathe.
Without oxygen, a turtle can live underwater for about three hours, depending on the species. But if you resurface every three hours, you can easily get caught by predators. Evolution has solved this problem. Some turtles have learned to breathe through their skin, others have special sinuses to help them absorb oxygen. Others have grown tubercles on their tongue and in their mouths that help them absorb oxygen from the water. Elusor macrurus, on the other hand, has learned to breathe through the cloaca.
However, in the turtle’s native Australia, it is called the Mary River, after the river where it lives. The locals nicknamed it the green-haired turtle because of the algae that grows on its shell and muzzle. The reason for this is a sedentary lifestyle, most of which the turtle just lies at the bottom of the river. Turtles eat everything that swims or sprouts nearby: algae, mollusks, fish and amphibians.
Now, about breathing in a little more detail. The thin skin of the hind mucosa is so thin that it can absorb oxygen from water. In other words, the turtle sucks in water with its cloaca, releases oxygen from it, and lets it out already without it. This helps turtles to remain unnoticeable mossy rocks.
Mary River is not the first turtle to learn how to breathe with its cloaca. There’s also Rheodytes leucops, which can stay underwater for about 13 hours. Intestinal breathing is a fairly common skill, also called enteric breathing.