Octopuses employ unique strategies to coordinate their bodies and arms while crawling around, researchers have found, with the creatures able to move in any direction relative to their body orientation.
Scientists at the Hebrew University of Jerusalem have reported the first detailed kinematic analysis of octopus arm coordination, showing that they have a unique motor control strategy which the central brain activates, rather than autonomous motor programmes in the peripheral nervous system of the arms.
The study, published in the Cell Press journal Current Biology, used videos of octopuses moving with researchers analysing them frame by frame.
Findings showed some surprise results – despite having a symmetrical body, they can crawl in any direction they want relative to its body orientation. The orientation of the body and crawling direction are independently controlled, while there are no apparent rhythmical patterns to the limb coordination.
Octopuses have weird bodies – they have a sophisticated brain in a soft, bilaterally symmetrical body with eight radially symmetrical and flexible arms.
They probably evolved from animals similar to clams, with a protective outer shell and virtually no movement: "During evolution, octopuses lost their heavy protective shells and became more manoeuvrable on the one hand, but also more vulnerable on the other hand," study co-author Guy Levy said. "Their locomotory abilities evolved to be much faster than those of typical molluscs, probably to compensate for the lack of shell."
They now have excellent vision, a highly developed and large brain and the ability to colour camouflage – making them excellent hunters.
Previous research has looked at goal orientated arm movements, used in feeding for example. The latest studies look at how they are able to coordinate their arms during normal travel.
With the videos, the team showed the unique manoeuvrability comes from the radial symmetry of their arms and the simple mechanism by which they create a crawling thrust – a simple pushing-by-elongation system. Taken together, the octopus only needs to choose which arms to activate in order to decide the direction of movement.
The authors conclude: "In summary, we believe that our findings provide a striking demonstration of the emergence of special control mechanisms well embodied within the unique morphology and flexibility of the octopus."
Researchers now plan to study the neural circuits involved in the octopuses' coordinated crawling.