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7 Mar, 2019 10:17

Animal discovered to have ‘on-demand anus’ that disappears when not in use

Animal discovered to have ‘on-demand anus’ that disappears when not in use

One of the most ancient types of creature on our planet may now become the butt of an evolutionary joke after it was discovered that the jelly has an ‘intermittent anus’ which appears and disappears on command.

The warty comb jelly, also known as a sea walnut, has no permanent connection between its gut and the rear of its body. Both its gut and its epidermis are just a single cell thick.

Instead, the jelly builds up waste in a bubble near its outer skin before a temporary anus opens up and expels the waste. Charming.


“It is not visible when the animal is not pooping,”explains Dr Sidney Tamm of the Marine Biological Laboratory. “There’s no trace under the microscope. It’s invisible to me.”


The jellies eat small crustaceans and baby fish and adults typically defecate once an hour. In addition, the species is also hermaphrodite, meaning this comb jelly can self-fertilize.  

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Warty comb jellies (Mnemiopsis leidyi) are from the phylum ctenophora group of ancient jellyfish-like organisms, believed to be over 500 million years old.

Ctenophores likely represent one of the most ancient forms of complex animals on the planet and research into their “transient anus” may shed light on the evolution of a permanent anus in invertebrates and, later, mammals.  

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