This first report of bipedal behavior in octopuses, written by University of California, Berkeley, researchers, will be published in the March 25 issue of Science.
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.
UC Berkeley graduate student 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.
The other type of octopus, which camouflages itself as algae in tropical waters from Indonesia to Australia, looks like a sea monster scooting along the sea floor on two legs. Huffard filmed this creature off Australia's Great Barrier Reef easily rolling over rocks and other obstacles.
"This behavior is very exciting," said Huffard, who first noted it five years ago in the coconut octopus but only recently was able to capture both types of octopuses on film. "This is the first underwater bipedal locomotion I know of, and the first example of hydrostatic bipedal movement."
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.