Two legs are better than eight when an octopus has a cunning escape strategy

They have eight legs and can move by jet propulsion but the octopus has another trick up its many sleeves - it can walk backwards on two legs as part of a cunning escape strategy.

They have eight legs and can move by jet propulsion but the octopus has another trick up its many sleeves - it can walk backwards on two legs as part of a cunning escape strategy.

Scientists have for the first time filmed bipedal walking in the octopus, which uses this unusual form of locomotion as an elaborate pretence at being an inanimate object.

One of the octopuses disguised itself as algal seaweed by dangling its other six legs around its head. The other curled its non-walking legs around its body to make it look like a fallen coconut shell.

Both carried out the mimicry while stealthily walking on their other two legs away from danger, said Crissy Huffard, a graduate student at the University of California at Berkeley who filmed them off Australia's Great Barrier Reef.

"This bipedal behaviour allows them to get away and remain cryptic," said Ms Huffard, whose pictures are published today in the journal Science . The octopus is essentially a water-filled balloon without a skeleton. It moves around and keeps its shape with the help of muscles acting on internal hydrostatic pressure.

"This is the first underwater bipedal locomotion I know of, and the first hydrostatic bipedal movement," she said.

Octopuses normally move around by crawling on all eight legs, using their suckers to push and pull them along. The species filmed walking on two legs used its limbs like the caterpillar tracks of a tank.