Pet turtles can be unsanitary. But Chinese soft-shelled turtles really up the ante on distasteful behavior. They perform a variation on urination—through their mouths.

Most land-based vertebrates produce urine to get rid of water-soluble toxic waste, notably nitrogen-containing urea. But researchers found that Chinese soft-shelled turtles get rid of just six percent of their urea through the kidneys. They also discovered a high concentration of urea in the turtles' saliva. Which led them to one place: the mouth.

Fish can remove waste through their gills, and these air-breathing turtles have gill-like structures in their mouths. Further research showed that they also have a urea-transporting protein that helps them get rid of it. The findings are in the Journal of Experimental Biology. [Yuen Ip et al., The Chinese Soft-Shelled Turtle, Pleodiscus sinensis, Excretes Urea Mainly Through the Mouth Instead of the Kidney]

When the turtles aren't able to go for long swims, they were seen spending well over an hour with their heads submerged in puddles. Apparently they were releasing the urea and cleaning out their mouths. And maybe just looking for a little privacy.

—Katherine Harmon

[The above text is a transcript of this podcast.]