An Atlantic longarm octopus. Photograph by John Forsythe

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An Atlantic longarm octopus.

An Atlantic longarm octopus. Photograph by John Forsythe

Atlantic Octopus Mimics Flounders—A First

An octopus in the Caribbean can mimic not only the shape of a flounder, but also the fish's color and swimming style, most likely in an attempt to avoid predators, researchers say.

A Caribbean octopus has been spotted disguising itself as a flounder, most likely in an attempt to avoid predators, researchers have announced.

Over the past decade, several Atlantic longarm octopuses have been captured on video imitating the sand-dwelling peacock flounder, mimicking not only the shape of the flatfish but also its color and swimming style.

Octopus mimics have been reported off the coast of Indonesia since 1998. (See a picture of an Indonesian octopus mimicking a sea star.)

This study marks the first case found in the Atlantic—and the fourth octopus species known to adopt a disguise. (Related: "Newfound Octopus Impersonates Fish, Snakes.")

Normally Atlantic longarm octopuses swim with their arms trailing behind their heads. But the newly released video shows the cephalopods folding their arms back into flounder shapes and undulating in a way that resembles flounder fins.

"It's a very athletic move," said study leader Roger Hanlon, of the Marine Biological Laboratory in Woods Hole, Massachusetts.

When stationary, the octopus seems content to just be itself. The animal only assumes flounder form when it's on the move, the scientists observed. (See pictures and watch video of "bizarre" octopuses that carry coconuts as instant shelters.)

Hanlon thinks the soft, squishy octopus uses flounder mimicry to avoid predators, which might be alerted to potential prey by motion.

A hungry sea creature might not think twice about biting off an arm or two from a passing octopus. But a rigid flatfish like a flounder would give a predator pause.

Octopus Hardwired for Flounder Form?

How exactly the octopus picked up its flounder-like behavior is still a mystery.

In the 1980s Hanlon had captured Atlantic longarm octopus larvae and brought them back to his lab, eventually raising one to adulthood. The captive animal displayed a weird swim pattern, but the scientists didn't recognize it as mimicry at the time.

When Hanlon saw the wild Atlantic octopuses "becoming" flounders like the species in Indonesia, he went back and looked at snapshots of the lab animal taken in 1985.

"It had never seen another octopus or a flounder, but it did this flounder mimicry," he said.

"We didn't know what that meant in the mid-1980s. But it gives a hint that there might be an innate component to this swimming behavior ... that maybe this is hardwired."

Overall, he added, the research shows that "camouflage is more than looking like the background. There are more sophisticated things going on here."

The research appears in the February issue of The Biological Bulletin.