Sometimes it seems really fun to be a turtle, all swimming around and retracting into your shell and not having to go to work and whatnot. And then you find out about the Chinese soft-shell turtle, which urinates through its mouth. Being a human doesn’t sound so bad now, does it?
Like us, this turtle has to excrete urea, which carries excess nitrogen out of the body. Humans do this via urine, which is urea plus water and other stuff you need to get rid of. The turtles do this too — 6 percent of the urea they excrete comes out as urine, from the usual places. But the rest of it, they basically spit into puddles.
While they’re in the water, the turtles can just hock up urea at will. But when on land, a Chinese soft-shell turtle will stick its head into whatever water it can find and expand and contract its mouth for up to 100 minutes, using gill-like structures inside the mouth to pump out excess urea. Science blogger Ed Yong explains why:
[Researcher Yuen] Ip thinks the answer lies in its salty habitat. To urinate through the normal kidney route, the turtle would need to constantly drink more water to make up for what it lost. And because the surrounding water is so salty, they would soon build up toxic levels in their bodies (especially since reptile kidneys are atrocious at getting rid of unwanted salts).
This method is pretty efficient — it gets rid of urea 15 to 20 times faster than the kidney-processing route. Still, if I had a chance to choose an animal trait to genetically enhance myself with, this would probably not be it.