'Penis fish' wash up on a beach in California

Thousands of creatures resembling penises have washed up on a beach in California.

The pulsating creatures are fat innkeeper worms, or Urechis caupo.

Although they are a type of worm, they are widely referred to as the "penis fish".

The worms bury themselves deep beneath the sand, but recent storms have uprooted them and Drakes Beach, about 50 miles north of San Francisco, has been covered in the creatures.

"Yes, the physical design of the fat innkeeper worm has some explaining to do. But the fat innkeeper is perfectly shaped for a life spent underground," wrote biologist Ivan Parr.

There is fossil evidence of the creatures dating back 300 million years and some live for up to 25 years, he added.

Within a beach, the creatures will dig a U-shaped burrows extending several feet long.

Their more polite nickname - innkeeper worm - comes from this subterranean lifestyle and the tunnels they create for other animals as they burrow underground.

Several other species, including fish, sharks, and otters feast on the penis fish.

And it's considered food for humans as well. Urechis unicinctus, the species found in East Asia, is a delicacy in countries including South Korea.