Thousands of 10-Inch 'Penis Fish' Washed Up on a California Beach

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A "penis fish" is neither a penis nor a fish. (Discuss.)

Try not to be alarmed by the thousands of plump, pink, 10-inch blobs caught flopping across a California beach last week. They are just some homeless penis fish.

Despite their nickname, a "penis fish" is neither a penis nor a fish. (Discuss among yourselves.) It's really a type of nonsegmented marine worm native only to the Pacific Coast between Southern Oregon and Baja California, Mexico. (The photo above was taken on Drakes Beach, north of San Francisco, on Dec. 6.) The blob's real name is Urechis caupo — but it's known more commonly as the "fat innkeeper worm." 

Related: 13 Strange Things That Washed Up on Beaches

The worm's unfortunate nicknames and its sausage-y shape are the result of hundreds of millions of years of building U-shaped burrows along the beach. These burrows, like all good homes, are for eating and pooping. 

From the front end of its burrow, the worm coughs up a net of mucus to catch tiny seaside nibbles like plankton, bacteria and other detritus that happen to pass by. When the worm sucks this net back into its mouth, it holds onto choice morsels and tosses the rest away through the back end of its burrow. It does this by spraying a jet of water out of its butt. (And you thought "penis fish" was funny.) 

Detritus that the penis fish deems unworthy may become a meal for other tiny beach denizens, such as crabs, shrimp and clams. In fact, it's common for a penis fish's burrow to host various opportunistic animals looking for a free bed and meal. This is where the worm's "fat innkeeper" nickname comes from.

Now, why might thousands of fat innkeepers end up wiggling around the beach at the same time? It's likely that a storm evicted them, biologist Ivan Parr wrote on BayNature.com, where the above photo was shared. Strong storms, especially those tied to El Niño, can wreak havoc on the intertidal zones where these worms rest their butts, breaking sand sediments apart, smashing thousands of cozy burrows and leaving their residents strewn across the beach.

Will the fat innkeeper economy every recover? It's not clear — the worm has not been studied enough to say for sure what happens next, Parr wrote. Further penis fish research is required.

Originally published on Live Science.

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Brandon Specktor
Brandon Specktor
Editor

Brandon is the space / physics editor at Live Science. With more than 20 years of editorial experience, his writing has appeared in The Washington Post, Reader's Digest, CBS.com, the Richard Dawkins Foundation website and other outlets. He holds a bachelor's degree in creative writing from the University of Arizona, with minors in journalism and media arts. His interests include black holes, asteroids and comets, and the search for extraterrestrial life.