It’s a bird … it’s a plane … it’s a penis fish?

Thousands of “pulsing penis fish” have washed ashore on a California beach, as seen in jarring photos that are raising eyebrows due to the creature’s phallic shape.

The quirky marine life is officially called fat innkeeper worms (Urechis caupo), and an expert writes for Bay Nature that he believes a recent storm in the Drakes Beach area is the reason so many of them mysteriously appeared on the beach.

Ivan Parr, a biologist from the Western Section of the Wildlife Society, spotted them Dec. 6 and explains that the 10-inch fat innkeeper worm typically lives underwater, burrowing in mud or sand, but the storm likely carried them ashore.

“I’ve heard my share of imaginative theories from beachcombers, such as flotsam of a wrecked bratwurst freighter,” he writes.

However, Parr explains that a sausage ship accident is not the cause of this scene.

“We’re seeing the risk of building your home out of sand,” he says. “Strong storms — especially during El Niño years — are perfectly capable of laying siege to the intertidal zone, breaking apart the sediments, and leaving their contents stranded on shore.”

The spoonworm, which can live up to 25 years, feeds and swims using its “spatula-shaped proboscis.” It typically eats bacteria, plankton and other small particles, which it collects using “sticky mucus nets.”

Parr says he’s heard of sightings over the years in California at Pajaro Dunes, Moss Landing, Bodega Bay and Princeton Harbor.

The creature dates back 300 million years and also can be eaten. An anonymous colleague at The Post who has dined on a stir-fried fat innkeeper worm in Shanghai, China, describes the taste as “like a Livestrong band mated with a clam.”