What is a warty comb jelly? © Alamy

What is a warty comb jelly?

Published: 16th April, 2022 at 11:00
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This translucent creature moves so slowly it's also known as the sea walnut.

Starter for 10: What’s 97 per cent water, eats its own offspring and has a ‘transient anus’? Meet the warty comb jelly, a cannibalistic creature with the world’s weirdest party trick. Most of the time, this jellyfish-like animal has no anus. Then, hey presto, just when it needs one, one magically appears, only to disappear moments later when defecation is done. It’s the only animal known to science to have such a bit of anatomy.


The anomalous animal, which is native to the east coast of America, belongs to a group of creatures called ctenophores. Members have translucent, blobby bodies and rows of iridescent cilia, which they use to propel themselves around the ocean and hoover up microscopic prey. But where other ctenophores have one, or sometimes even two permanent bottom holes, the warty comb jelly has an ephemeral orifice that comes and goes.

When it needs to poo, part of its gut fuses with the outer epidermal layer, which then puckers up to form the fleeting orifice. Adults the size of golf balls go with reassuring regularity, around once an hour, and if it all sounds like a crock of excrement, think again. Scientists believe the arrangement may represent an intermediate stage in the evolution of the anus.

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Helen Pilcher
Helen PilcherScience writer, presenter and performer.

Helen Pilcher is a tea-drinking, biscuit-nibbling science and comedy writer, with a PhD in cell biology.


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