Turtles are fascinating creatures, and their breathing system is just one of the many unique features that make them so intriguing. Unlike most vertebrates, turtles do not have a flexible rib cage that allows their lungs to expand and contract during breathing. This is because they have a protective shell that evolved to replace their flexible ribs. But how do turtles breathe without a flexible rib cage?
The lungs of a turtle are located just beneath the carapace and above the other internal organs. The upper surface of the lungs attaches to the carapace, while the lower portion is connected to the viscera by a skin of connective tissue known as diaphragmatic. The viscera are also contained within a membrane that attaches to the diaphragmatic. Groups of muscles rhythmically change the volume of the abdominal cavity to move the viscera and ventilate the lungs.
When turtles walk about, the motions of their forelimbs promote the suction and compression actions that ventilate the lungs. By drawing their limbs inward and then extending them outward, turtles can change the volume of their lungs and breathe. Turtles floating on the water's surface can be seen moving their legs in and out to help them breathe.
But turtles have other strategies to obtain oxygen as well. The hyoid apparatus, a system of bony and cartilaginous rods located at the base of the tongue, is one aid to respiration. Raising and lowering the hyoid apparatus causes a turtle's throat to rise and fall, pulling in air. Soft-shell turtles, in particular, have a unique strategy to obtain oxygen while underwater. They have finger-like projections of skin called villi lining their throats that work like gills, expelling carbon dioxide and taking in oxygen from the water. Soft-shell turtles use their hyoid apparatus to repeatedly fill and empty their throat, a process known as buccopharyngeal breathing, to process oxygen-rich water.
It's also interesting to note that turtles that hibernate underwater exchange gases through their throat lining, cycling the water inside the throat cavity several times each minute. Some turtles even take in oxygen through the cloaca, a unique adaptation that allows them to obtain oxygen while submerged in water.
Despite the many unique adaptations turtles have evolved for breathing, many details of their breathing system remain unknown. One thing that is clear, however, is that turtles are experts at obtaining the oxygen they need to survive. Their diverse range of breathing strategies is a testament to the incredible adaptability of these ancient and fascinating creatures.