An Amphioctopus marginatus has been observed using coconut shells as armor. Here is a picture PZ Myers has on his blog of the species:
“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,” [Australian zoologist Julian] Finn said. “It was an extremely comical sight—I have never laughed so hard underwater.”
This is apparently significant because it carried the coconuts to a certain location for a specific use, which is something never seen by sea creatures before. Birds and some mammals do it, too, so it’s not that crazy, really. We all know that African swallows can carry coconuts across oceans as long as they grip it by the husk.
I guess we should all make our arrangements now then. Not only can they use tools, but they can also walk bipedally. It’s only a matter of time before the veined octopuses of the world enslave us all.
UPDATE: Here is a video of the octopus which made the zoologist lol: