Octopuses ‘walk’ on 2 arms to get by predators

From octopus to soft robot
A walking octopus whose legs require limited guidance from the brain excites Science coauthor Robert Full from the University of California, Berkeley.

This discovery adds to our growing understanding of how soft-limbed creatures perform complex behaviors without too much communication between limb and brain. A better understanding of how walking octopus arms work could help scientists design better artificial materials and improved soft robots, Full said.

“This discovery provides true inspiration for the beginning of a new age of soft robotics. The videos are almost unbelievable,” Full said.

A walking octopus also provides another chance for scientists to study the interactions animals with soft limbs have with their environment, explained Full, who is also intrigued by how elephants use their soft trunks.

Algae and coconuts
The “algae octopus” is no stranger to life in the algae impersonation business. When they are not moving, their long arms and walnut-size bodies look like algae. This is the first time, however, scientists have seen an octopus take this algae impersonation show on the road.

Not surprisingly, Octopus marginatus has prior coconut experience. This species is known to crawl inside empty coconut shells for shelter, pulling the two sides of the shell together with the suckers on their arms.

According to local diving lore from Indonesia, octopuses inside real coconut shells will stick their arms out of the shells and walk around, Huffard said. While this may be just a story, the scientists caught plenty of curious octopus muscle activity on video.

A muscle beach without ego
The most amazing muscles at the beach are not flexed by the people playing sand volleyball.

Bands of muscle in the octopus arms are oriented in three directions. The muscle contractions start near the top of the walking arms and move down to the tips of the arms. These waves of muscle contractions give the arms the flexibility they need for walking, the authors suggest. The fluid filling the muscles provides stability.

When the “coconut octopus” rolls along the sand on its back two arms, these fluid-filled muscular limbs serve as conveyor belts. At least one of these conveyor belts is on the ground at all times, which qualifies the movement as walking.

The arms of the “algae octopus” move in a somewhat similar fashion but they hold the other six arms in a different manner. Imagine a ragged head of broccoli running along the bottom of the ocean.

Huffard hopes to return to Indonesia and Australia in the near future to continue studying these walking octopus species.

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