Image: Monika
Korzeniec/Wikimedia
Everything pees, even the weird-looking Chinese soft-shelled turtle. But not everything pees through its mouth, unlike the aforementioned creature:
When the turtle breaks down proteins in its liver, it ends up with an abundance of nitrogen, which it expels from its body in the form of urea. Humans are the same—we get rid of urea in the form of urine, via our kidneys. But the soft-shelled turtle has an altogether different route.
It’s well-adapted to life in the water, and lives in salty swamps and marshes. But Yuen Ip from the National University of Singapore noticed that when the turtle emerges from water, or is stranded on land during dry spells, it will plunge its head into puddles. While submerged, it rhythmically expands and contracts its mouth. Ip found that the turtle gets rid of most of its urea through its mouth rather than its kidneys, via gill-like studs in its mouth. It can breathe and urinate through the same structures.
Ed Yong of Not Exactly Rocket Science explains: Link