How to use 8 arms? Octopuses tend to explore with their front limbs

WASHINGTON (AP) — Humans may be right-handed or left-handed. It turns out octopuses don't have a dominant arm, but they do tend to perform some tasks more often with their front arms, new research shows.

Scientists studied a series of short videos of wild octopuses crawling, swimming, standing, fetching, and groping -- among other common activities -- to analyze how each of the eight arms were moving.

“All of the arms can do all of this stuff – that’s really amazing,” said co-author and marine biologist Roger Hanlon of the Marine Biological Laboratory in Woods Hole, Massachusetts.

Octopus limbs aren’t specialized as many mammal limbs are. However, the three octopus species in the study showed a clear preference for using their four front arms, which they did about 60% of the time. The back arms were used more frequently for stilting and rolling that help move the octopus forward.

“The forward arms do most of the exploring, the rear arms are mostly for walking,” said Mike Vecchione, a Smithsonian National Museum of Natural History zoologist who was not involved in the study.

Researchers analyzed video clips taken between 2007 and 2015 in the Atlantic Ocean and Caribbean Sea. It was the first large study to examine precise limb actions in the wild.

Unlike previous research of octopus behavior in a laboratory setting, the new work showed that octopuses did not show a preference for right or left arms in their natural environment.

Results were published Thursday in Scientific Reports.

“I’m in awe that the researchers managed to do this,” said Janet Voight, an octopus biologist at the Field Museum of Natural History in Chicago, who had no role in the study.

Octopuses are shy and elusive creatures. The species studied spend most of their time hidden in dens — meaning that filming them required patience and perseverance over many years.

Octopus limbs are complex — used for mobility and sensing the environment. Each arm contains between 100 and 200 suckers – complex sensory organs “equivalent to the human nose, lips, and tongue,” said Hanlon.

If an arm is bitten off by a predator, as often happens in the wild, octopuses have multiple backups.

“When you've got eight arms and they're all capable,” Hanlon said, “there's a lot of redundancy.”

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