The Giant California Sea Cucumber uses its anus as second mouth.
Recent research has found that the Giant California Sea Cucumber (Parastichopus californicus) can use both ends of its body to feed and breathe.

“P. Californicus” is shaped like a hollow tube, with a mouth at one end and its anus at the other. It utilises a technique defined by scientists as ‘bipolar feeding’ to increase its chances in search for food.
A 50-centimeter-long (20-inch-long) animal can pump 3.5 to 4 cups of water per hour through its anus, simply utilising the muscles of their cloaca.

It has long been known to science that sea cucumbers are able to absorb oxygen with their backside. These animals don’t have lungs. Instead, they use respiratory trees to respire. These tubes branch and run down both sides of the sea cucumber’s cylindrical body. When water enters the sea cucumber’s anus, the respiratory trees take in the oxygen and distribute it to the sea cucumber’s cells.

The respiratory trees of the sea cucumber are connected to the gut by a group of blood vessels called the rete mirabile. It was initially thought that the rete mirabile was used to oxygenate the gut cells. However, recent research has shown that this animal is able to feed through its rear by transporting food to the gut using these blood vessels.

So far, evidence of such behaviour has only been tested in the giant California Sea Cucumber, it is possible that many other species use the same technique.

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