Stealthy Bipedal Octopuses -- Miller 2005 (324): 3 -- sciencenow:
That's why the behavior of [Octopus] aculeatus is so fascinating, says Christine Huffard, a graduate student at the University of California, Berkeley, who led the new study. The octopus can scurry along the seafloor on the tips of two arms--planting one "foot" before the other in a motion surprisingly reminiscent of human walking--while it keeps its other six arms extended in a fairly convincing algae imitation (see links below).
In the 25 March issue of Science, Huffard and colleagues also report that an Indonesian octopus, O. marginatus, performs a similar trick, walking on two arms with its other arms balled up beneath its body. The researchers interpret this behavior, perhaps somewhat imaginatively, as an impression of a rolling coconut. Both octopuses can move slightly faster in stealth mode than they can when crawling with several arms, another possible advantage, Huffard says.
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. Camouflage is classic natural selection at work. These are co-evolved with aspects of their environment.