The bizarre turtle that urinates through its mouth... and is a delicacy in Chinese restaurants
- Chinese soft-shelled turtle is the only creature to excrete through its mouth
- Researchers say it evolved like this to survive in brackish swamp waters
If aliens from outer space visited our planet, they might be surprised to find that we excrete waste through our genitals - which, of course, also have a vital use in reproduction.
However, the Chinese soft-shell turtle has evolved to use a very different orifice to rid itself of waste .
Most usually encountered at upmarket restaurants in China, where they are considered a delicacy, these unusual amphibians are the only animals known to urinate through their mouths.
Wash your mouth out! The Chinese soft-shelled turtle is the only animal known to science that actually urinates through its mouth
Now scientists believe that this apparently unique ability helped the animals adapt to survive in swamps and marshes where the water is often brackish - that is, slightly salty.
Scientists in the 19th Century discovered that the linings of the mouths of soft-shelled turtles are covered with tiny, finger-shaped protrusions.
Subsequent research revealed that these allow the turtles to breathe underwater by increasing the surface area of the mouth where oxygen and carbon dioxide can be exchanged.
But Alex Yuen Kwong Ip of the National University of Singapore believes that these characteristics evolved for one reason only: to help the turtles urinate through their mouths more easily.
UNUSUAL CHINESE DELICACIES
Here are some other Chinese delicacies that might seem odd to Western diners:
- Snake head soup
- Solidified duck blood
- Cow’s lung soaked in chilli sauce
- Goat genitals soup
- Goat foetus
- Deep fried bee larvae
- Dog stew
Together with Shit Fun Chew of Singapore's Nanyang Technological University, Professor Ip kept four turtles in tanks of water for six days, New Scientist reported.
Each animal had a tube attached to its cloaca, the posterior opening where amphibians usually excrete both urine and faeces, so Professor Ip could keep tabs on what emerged.
The researchers found that, incredibly, only 6 per cent of the turtle's urea came out of the cloaca, with the rest mysteriously turning up in the tank's water.
Professor Ip also restrained the turtles on land. He found that when he placed a bucket of water in front of them the creatures plunged their heads in for between 20 and 100 minutes.
Observing more closely, he watched as they held some water in their mouths for a while then spat it out, increasing the concentration of the urea in the water.
Delicacy: Chinese soft-shelled turtles are farmed across South East Asia, where they are considered a delicacy and are often served in upmarket restaurants
Professors Ip and Chew found that proteins in the turtle's mouth lining help to transport urea from its bloodstream. They managed to isolate on such protein and found it was only present in the mouth and not the kidney.
'I know of no other animal that can excrete urea through the mouth,' Professor Ip was quoted by New Scientist as saying.
Most fish excrete through their gills, and lungfish and some amphibians can do so through their skin, but the Chinese soft-shelled turtle's oral excretion is almost certainly a one-off.
Professor Ip believes oral urination helped the turtles adapt to life in brackish waters. To excrete urea via their kidneys and through their cloaca they would need to drink a lot of water to flush it through.
That would mean consuming a lot of salt, which would be difficult for them to get rid of. So instead of drinking the backish water, the turtles are able to simply rinse their mouths with it.
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