You Won't BELIEVE How Some Turtles Breathe Underwater!

While most creatures rely on lungs or gills for obtaining vital oxygen, certain freshwater turtles possess a truly remarkable adaptation for underwater survival. These fascinating reptiles, including species like Australia's Fitzroy River turtle, can absorb oxygen directly from the water (Review) through specialized structures located in their cloaca, a multi-purpose opening at their rear end. This unique form of gas exchange, known as cloacal respiration, allows them to remain submerged for extended durations, a strategy that offers significant benefits in their aquatic environments.

The scientific explanation behind this unusual ability lies in the anatomy of these turtles. Within their cloaca, they have developed two sac-like extensions called bursae. These bursae are richly supplied with blood vessels and lined with numerous tiny, finger-like projections known as papillae, which greatly increase the surface area available for gas exchange. By rhythmically contracting their cloacal muscles, these turtles can actively pump water into and out of these bursae. As water flows over the papillae and their dense network (Review) of capillaries, dissolved oxygen diffuses across the thin membranes into the turtle's bloodstream, while carbon dioxide is released into the water.

This extraordinary method of "breathing" provides a crucial survival advantage. It enables turtles to stay underwater for hours, days, or even months, especially during colder periods when they enter a state of brumation, similar to hibernation. During these times, their metabolic rate significantly slows, reducing their oxygen demand, which can then be met by cloacal respiration alone. This adaptation also allows them to avoid surface predators or forage in deeper waters without the constant need to return to the surface for air, though it serves as a supplement to, rather than a complete replacement for, their primary lung respiration.