An octopus’s arm is covered with hundreds of suckers that give it a strong tendency to attach to everything it encounters but the octopus’s arms. A team of researchers has shown that chemical signals from the skin of octopus protect its arms from attaching to each other or onto themselves, without which the octopus might end up entangled.

The team studied the behaviour of severed octopus arms — which remain active and move for at least an hour following separation — because arms have their own network of neurons that to some extent can work independent of the central control of brain.

Suckers on severed arms — like the ones on intact arms — attached to any surface but avoided the skin. They did attach to another arm but only at points where the skin was damaged or missing, suggesting that the skin, wherever present, might play a role in inhibiting the attachment.

When arms were presented with petri dishes partly covered with octopus skin, its suckers avoided the skin, attaching only to exposed parts of the dish. To pin down if chemicals in the skin inhibit suckers from attaching to it, the researchers then presented the arms with petri dishes, this time coated with a gel made from crude extracts of octopus skin dissolved in a solvent.

Suckers grabbed the petri dishes coated in skin extracts with a force that was about 10 times weaker than with which suckers attached to a ‘control’ — petri dishes coated with just the solvent, they report in a paper published in the journal Current Biology on May 15.

“This is due to a chemical self-recognition mechanism,” said Guy Levy, co-author of the study and a researcher at The Hebrew University of Jerusalem, Israel.

“There are receptors on the rim of suckers, like receptors we have on our tongue or in our nose to taste or smell. The octopus uses these receptors to sense and investigate materials it encounters in its environment,” he said. Levy and co-workers now plan to identify the chemical that aids in this self-recognition mechanism.

(The author is a freelancer based in Bangalore)

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