Thousands of fat innkeeper worms, known as “penis fish,” have washed up on a beach in Northern California.

An image of the worms was posted on Instagram by Bay Nature magazine on Dec. 6.

“Thousands of these marine worms—called fat innkeeper worms, or ‘penis fish’—were found on Drake’s Beach last week!” said the magazine. “These phallic organisms are quite common along the West coast of North America, but they spend their whole lives in U-shaped burrows under the sand, so few beachgoers are aware of their existence.”

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In an article, Bay Nature magazine explained that the pulsating 10-inch worms may have been washed up by a strong storm that disrupted sediments in the intertidal zone.

Innkeeper worms, or Urechis unicinctus, are also found in the Elkhorn Slough nature reserve on Monterey Bay, California.

"It lives in a ‘U-shaped’ tunnel or burrow and has a unique method of eating. It secretes a slime net, which serves to trap small food particles,” explains NOAA. “The worm circulates water through the tunnel, trapping food in the slime net. When the mucus net becomes loaded with food, the entire net, with its burden of food, is swallowed by the worm.”

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The worms can reach up to 19 inches long, but are usually six to nine inches long, according to NOAA.

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