Two species of tropical octopus have evolved a neat trick to avoid predators - they lift up six of their arms and walk backward on the other two.
When walking, these octopuses use the outer halves of their two back arms like tank treads, alternately laying down a sucker edge and rolling it along the ground. In Indonesia, for example, the coconut octopus looks like a coconut tiptoeing along the ocean bottom, six of its arms wrapped tightly around its body.
Crissy Huffard clocked the two-legged speed of one coconut octopus at two and a half inches per second, while a second individual zoomed along, backwards, at five and a half inches per second. This is faster than they can crawl, but probably slower than they jet around.
Huffard and coauthor Robert Full, professor of integrative biology at UC Berkeley, think that this bipedal walking is a strategy octopuses use to backpedal away from predators while remaining camouflaged. Octopuses camouflage themselves by changing both color and shape, but when startled and forced to move quickly, they have to give up their camouflage.
Not so when walking.
"This bipedal behavior allows them to get away and remain cryptic," said Huffard.
Both Huffard and Full are interested in how these octopuses control their unusual form of bipedal locomotion. Recent articles shed light on this. Israeli scientists have reported that octopus arms execute incredibly complex curling and bending motions even when cut off. Apparently a nerve ganglion in each arm can send clock-like signals down the arm to produce rhythmic movements, such as bends propagating down the arm, irrespective of whether there is a head and brain to control them. Similar movements seem to be involved in two-legged walking.
"These are stereotyped movements that don't need feedback from the brain," Huffard said.http://crissyhuffard.com/bipedal-octopuses.htmlhttp://en.wikipedia.org/wiki/Amphioctopus_marginatushttp://jeb.biologists.org/content/209/19/3697.full