Why Don't Octopus Tentacles Suction Their Own Bodies? Scientists Know.

By Shweta Iyer on May 15, 2014 1:21 PM EDT

octopus
Why don't octopus tentacles suction their own bodies? Scientists know. (Photo: Photo courtesy of Shutterstock)

Nature is the perfect engineer. Just like it designed snakes so that they don't poison themselves with their own venom, it created octopuses such that they don't stick their four pairs of arms with their suction pumps to their own bodies. Now, researchers from the Hebrew University of Jerusalem have tried to uncover the physiognomy behind this engineering. Their research is published in Cell Press publication Current Biology on May 15, according to a press release Thursday..

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Circular suckers cover the octopus's arms, which enables them to cling to things, grasp prey, and other objects. But they can keep their arms from attaching on themselves. This not a conscious act as their brains don't control the movement of their arms but the action of a chemical produced by octopus skin that temporarily prevents their suckers from sucking.

"We were surprised that nobody before us had noticed this very robust and easy-to-detect phenomena," says Guy Levy, who carried out the research with co-first author Nir Nesher. "We were entirely surprised by the brilliant and simple solution of the octopus to this potentially very complicated problem."

Binyamin Hochner, who has been studying body motor control on octopuses for several years says that there is a reason why they are not aware of their arms like humans or other animals are, "Our motor control system is based on a rather fixed representation of the motor and sensory systems in the brain in a formant of maps that have body part coordinates," he says. This is so because we have rigid bones.

But, according to Hochner, "It is hard to envisage similar mechanisms to function in the octopus brain because its very long and flexible arms have an infinite number of degrees of freedom. Therefore, using such maps would have been tremendously difficult for the octopus, and maybe even impossible."

So, if octopuses are unaware of their arms then what prevents the arms from sticking to their bodies?To understand this, researchers studied the behavior of amputated octopus arms that remain active for up to an hour after separation. The arms grabbed octopus arms that had been skinned but did not grab octopus skin. The octopus arms didn't grab Petri dishes covered with octopus skin, either, and they attached to dishes covered with octopus skin extract with much less force than they otherwise would.

"The results so far show, and for the first time, that the skin of the octopus prevents octopus arms from attaching to each other or to themselves in a reflexive manner," the researchers write. "The drastic reduction in the response to the skin crude extract suggests that a specific chemical signal in the skin mediates the inhibition of sucker grabbing."

But live octopuses can behave differently when it suits them. They can grab an amputated arm if they want and they are more inclined to so if the arm belongs to someone else. Although the chemical processes that go in to this self-avoidance yet needs to be studied, researchers attribute it also to the octopus' intelligence. This trait, they say, can be used for robotic designs.

"Soft robots have advantages [in] that they can reshape their body," Nesher says. "This is especially advantageous in unfamiliar environments with many obstacles that can be bypassed only by flexible manipulators, such as the internal human body environment."

With this aim, the researchers have shared their findings with European Commission project STIFFFLOP, to develop a flexible surgical manipulator in the shape of an octopus arm. "We hope and believe that this mechanism will find expression in such new classes of robots and their control systems," Hochner says.

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