Why This Octopus Isn't Stuck-Up

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The octopus is famous for, what else, eight arms, each of which has hundreds of suckers. Scientists have been studying how octopuses control all those weird appendages. It was recently discovered that one simple trick helps keep the arms from sticking to each other and getting tied up in knots. NPR's Nell Greenfieldboyce untangles it for us.

NELL GREENFIELDBOYCE, BYLINE: Scientists who study octopuses say these animals are so strange they might as well be from another planet.

FRANK GRASSO: They still have the same kinds of problems that we do but with a very different body, a very different brain architecture and, therefore, in a very alien way.

GREENFIELDBOYCE: Frank Grasso studies octopuses at Brooklyn College in New York. He says an octopus does not control its arms in the same way that you control your arms.

GRASSO: Like if you were to be blindfolded, you know, and move your arms around, you'd have a very good idea of where your arms were. You'd have, like, a mental image.

GREENFIELDBOYCE: He says octopuses don't have that mental image of every arm. Instead, the arms themselves control a lot of their own movement. They kind of have minds of their own. If you chop off an octopus arm, it will live for more than an hour. It'll grab things and latch on with its suckers. So, this raises a question: as an octopus moves through the water and the arms all brush up against each other, why don't the suckers on one arm latch onto another arm and get the octopus all tangled up?

GRASSO: Three hundred suckers on eight arms that all need to be coordinated. We all said to ourselves, why hasn't anybody thought of this before?

GREENFIELDBOYCE: Grasso has been working with scientists at the Hebrew University of Jerusalem in Israel, who recently did some experiments with amputated octopus arms. First, they checked to see if the suckers on any given arm would stick to any other octopus arm. It turned out they wouldn't. Then the researchers took a plastic lab dish and covered it with octopus skin. They found that an arm's suckers wouldn't grab that either. But when they left part of the dish uncovered, the suckers would grab onto that part's plastic surface. All this suggested that octopus suckers are repelled by something in octopus skin.

GRASSO: There seems to be a chemical detection capacity built into the rims of the suckers to recognize octopus skin and inhibit attachment.

GREENFIELDBOYCE: Experiments with a crude extract from skin confirmed that.

GRASSO: And it's a nice little trick that solves a problem that evolutionarily these animals have probably faced for 505 million years.

GREENFIELDBOYCE: Grasso and his colleagues in Israel who did the experiments describe all this in the journal Current Biology. Nell Greenfieldboyce, NPR News.

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