Meet the soft-shelled turtle that urinates from its mouth

This is the "strangest thing you'll read all day," says Eric Berger at the Houston Chronicle. Chinese soft-shell turtles have a curious habit that has long perplexed biologists: They sometimes submerge their heads underwater for more than an hour. Now, for the first time, scientists know exactly what the turtles are doing down there — taking a bathroom break in which they urinate from their mouths. Here's what you need to know:

What kind of turtles are we talking about?

These Chinese soft-shelled turtles are "commonly encountered as food in upscale restaurants," says Michael Marshall at NewScientist, and are widely farmed throughout Southeast Asia. Out in the wild, they live in swamps and marshes where the water is often "brackish," or "salty, but not as salty as seawater."

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And they really pee out of their mouths?

Basically. In this experiment, published in the Journal of Experimental Biology, scientists purchased a couple turtles from their local Chinatown in Singapore. The turtles were put in tanks and given a shallow puddle they could submerge their heads into, which they would sometimes do for 100 minutes at a time. After the turtles were done, scientists tested the water, which was filled with urea, "the main waste product found in urine," says Charles Choi at LiveScience. This secreted urea doesn't replace normal peeing — the turtles still go to the bathroom the regular way, too — but 50 times more urea came out of turtles' mouths than genitalia. Once the turtles were done mouth-peeing, they'd take a gulp of water, swish it around, and spit it back out.

Why is this advantageous?

The team thinks the strange ability allowed the turtle to live in salty underwater environments. Salt water is, of course, undrinkable. And traditional urination requires the turtle to drink loads of freshwater to flush itself out. But secreting urea from the mouth, on the other hand, can be done without drinking a bunch of water, says Ian Chant at Geekosystem.

Does any other animal do this?

"I know of no other animal that can excrete urea through the mouth," says researcher Alex Yuen Kwong Ip. A few varieties of fish can urinate through their gills, and some amphibians rid themselves of urea through their skin. At least for now, however, the Chinese soft-shelled turtle's bathroom habits are truly one of a kind.

Sources: Geekosystem, Houston Chronicle, LiveScience, NewScientist