WALNUT CREEK, Calif. – Looking a bit like a cartoonist’s effort to make strange sea creatures seem more human, two species of octopus have been caught on tape walking on just two of their eight legs.

One species wraps six of its legs around itself in a tight ball as it jogs backwards across the sea bed on the other two, somewhat like a little green video game alien trying to avoid being eaten or shot. The other holds six arms up in frozen, crooked poses like tree branches as it moves on two arms that seem to act like mini conveyor belts.

The Bay Area biologist who discovered the strange behavior suspects it may be a clever way for the animals to disguise themselves from predators while on the move.

“They are able to do two things at once, camouflage and walk, which is fairly unique for an octopus,” said Christine Huffard a UC Berkeley graduate student who has been studying the creatures for nearly a decade.

Her findings will be published Friday in Science.

Huffard first spotted a walking octopus years ago while assisting another scientist studying coral reef recovery in Indonesia. She was diving with a film crew who captured the bizarre behavior and let Huffard use the footage for her research.

The Indonesian octopus is known to local divers as the coconut octopus because it likes to hide in the coconut shells that litter the sea bed. Huffard thinks the animals may be wrapping their arms into a ball in an attempt to imitate a rolling coconut to avoid catching the eye of a shark, sting ray or scorpion, while on the move.

“It would be completely possible that it is camouflaged as a coconut,” Huffard said.

She was helping another scientist working on mantis shrimps on Lizard Island, Australia when she found the octopus that her research was focused on, commonly known as an algae octopus. She caught one and had it in a large tank when it started to walk backward, looking like a clump of algae drifting in a current.

Normally, octopuses either crawl along using several arms sprawled around their body and their suckers to pull and push themselves along, or they swim. The walking behavior is faster than crawling and slower than swimming. But two-legging it may have the considerable advantage of keeping the octopus hidden while still allowing it to get around at a reasonable speed instead of creeping at a snail’s pace to avoid being conspicuous.

Armed with tape of the two walking octopuses, Huffard went last year to Robert Full in the biomechanics lab at UC Berkeley. Full encouraged her to publish her observations and co-authored the paper being published Friday.

“He couldn’t believe it,” said Huffard. “He just kept saying, “I don’t believe this, I don’t believe this, I don’t believe this.”‘

Walking on two legs is generally reserved for animals with skeletons, and it had been thought that the opposition of muscle against rigid bones was required for this kind of locomotion. The octopuses apparently use opposing bands of muscle and a rolling motion that carries a bend down the arms like a wave to accomplish the feat.

“Understanding behavior like this could usher in a new frontier of “soft’ robotics,” in contrast to the rigid robots common today,” Full said in a release from UC Berkeley.

The coconut octopus had been spied walking by local divers before Huffard got her first look, and she suspects their may be other eight-leggers out theshe said. “They’re just fascinating animals.”


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