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A scientist has discovered an unusual feature on the morphology of a jellyfish-like creature—an “intermittent anus” that disappears after it defecates.

Mnemiopsis leidyi is a type of ctenophore—also known as a comb jelly. While native to western Atlantic coastal waters, it is one of the world’s most invasive species and has established itself in regions around Europe and Asia.

The species has been the subject of much scientific research. Comb jellies, such as Mnemiopsis leidyi, evolved more than 500 million years ago. The first animals on Earth did not have a dedicated anus—a separate opening for waste turned up far later in the evolutionary timeline. Instead, these ancient creatures had one opening that served as both their mouth and anus. Many of their descendents alive today still have this digestive set-up.

Having a separate mouth and anus is advantageous evolutionary speaking—it allows an animal to eat and digest at the same time, rather than having to finish a meal before starting the digestive process. 

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