How the Octopus Stays Untangled: Coordination Made Elegantly Simple

The octopus is one heck of an intriguing animal, scuttling along the ocean floor or swimming through the deepest, darkest waters with a beautiful, yet alien-like grace. But can you imagine being one? That's a lot of limbs to keep track of all at once, and yet these animals somehow never tangle themselves up. How do they pull it off? A team of researchers from The Hebrew University of Jerusalem think they have the answer.

"Octopuses use unique locomotion strategies that are different from those found in other animals," researcher Binyamin Hochner said in a recent release. "This is most likely due to their soft molluscan body that led to the evolution of 'strange' morphology, enabling efficient locomotion control without a rigid skeleton."

Hochner, alongside two of his colleagues, recently authored a new study on octopus limb coordination and locomotion, which was published in the journal Current Biology. They describe how, like everything else about the octopus, its strange and agile way of getting around is likely a consequence of its unexpected evolutionary history - in which squishy cephalopods' ancestors were likely once more like rigid and immobile clams.

"During evolution, octopuses lost their heavy protective shells and became more maneuverable on the one hand, but also more vulnerable on the other hand," explained co-author Guy Levy. "Their locomotory abilities evolved to be much faster than those of typical molluscs, probably to compensate for the lack of shell."

If you look at most clams and snails, they stiffly move along with a single slow, but powerful foot. Somehow, in the mysterious ways of genetic mutation and natural selection, this appendage eventually developed into the long and slender arms that we see today. But knowing this does little to explain how exactly octopuses control them with such deft.

To find out why, Hochner, Levy, and their colleagues poured over videos of octopuses in action, frame by frame. They determined that the orientation of its body is utterly independent of which direction it's moving. Additionally, when the animal crawls along the seafloor it lacks any predictable rhythm - unlike spiders or crabs.

According to the study, the secret is that an octopus does not move itself by pushing or pulling in one direction, but instead allocates different arms for different directions (ie - to head right, the two left-most arms might push off the floor while the others simply stay out of the way).

With this surprisingly simple system revealed, the team now hopes to uncover the neural circuits involved in the octopus' coordinated crawling.

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