After years of surprising scientists with their cleverness and smarts, some octopuses appear to also use tools.

Veined octopuses observed off the coast of Indonesia carried coconut shell halves under their bodies, and assembled them as necessary into shelters — something that wasn't supposed to be possible in their corner of the animal kingdom.

"To date, invertebrates have generally been regarded as lacking the cognitive abilities to engage in such sophisticated behaviors," wrote Museum Victoria biologists who described the octopuses in a paper published Monday in Current Biology. "The discovery of this octopus tiptoeing across the sea ﬂoor with its prized coconut shells suggests that even marine invertebrates engage in behaviors that we once thought the preserve of humans."

In captivity, some species of octopuses have solved mazes, remembered cues and passed other cognitive tests typically associated with advanced vertebrates. More anecdotally, they're known for popping aquarium hoods, raiding other tanks and demonstrating what might be called mischief.

All this has come as a bit of a surprise to scientists. After all, octopuses are descended from mollusks. They're more closely related to clams than to people. They're not supposed to be smart. But it's hard to argue with the evidence, and in recent years, researchers have grappled with the possibility that octopuses can even use tools.

That debate has focused on octopuses seen barricading their den openings with stones. In the end, that behavior wasn't accepted as genuine tool use, because it seemed more instinctive than calculated. (Another contested invertebrate behavior is the use of shells as homes by hermit crabs. According to the conventional wisdom, tools require direct manipulation, so the shells are no more tools than are human houses.)

Such definitions are inevitably ambiguous. But there's no ambiguity in the veined octopuses found flushing mud from buried coconut shells, stacking them for transport — an awkward process that required the octopuses to walk on tiptoe with the upturned shells clutched beneath them — and finally turning them into hard-shelled tents.

"The fact that the shell is carried for future use rather than as part of a speciﬁc task differentiates this behavior from other examples of object manipulation by octopuses," wrote the researchers.

With their tents, the veined octopus has joined chimpanzees, monkeys, dolphins and crows in the ever-expanding menagerie of non-human tool users. But as significant as the finding may be, the moment of discovery wasn't exactly solemn.

“I could tell that the octopus, busy manipulating coconut shells, was up to something, but I never expected it would pick up the stacked shells and run away. It was an extremely comical sight," said Julia Finn, a Museum Victoria biologist, in a press release. "I have never laughed so hard underwater.”

Image: At top left, a veined octopus; bottom left, a veined octopus carrying its shells; at right, inside the assembled shell house/Current Biology.

Video: Julian Finn/ Museum Victoria

See Also:

Citation: "Defensive tool use in a coconut-carrying octopus." By Julian K. Finn, Tom Tregenza and Mark D. Norman. Current Biology, Vol. 19 No. 23, December 15, 2009.

Brandon Keim's Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecosystem and planetary tipping points.