"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.