Octopus carries around coconut shells as suits of armour

Octopuses are masters of camouflage that can change their shape, colour and texture to perfectly blend into their environment. But the soft bodies that make them such excellent con artists also make them incredibly vulnerable, should they be spotted. Some species have solved that problem with their fierce intellect, which allows them to make use of other materials that are much harder. The veined octopus, for example, dons a suit of armour made of coconut shells.

The veined octopus (Amphioctus marginatus) lives in sandy, exposed habitats that have little in the way of cover. To protect itself, it hides among the hollow husks of coconuts. It even carries its armour around with it, tucking the shell under its body, sitting on it like a bowl, and moving around on tip-tentacles.

These cumbersome hikes can last for up to 20 metres and they make the octopus look like an eight-legged stilt-walker. The octopus can even carry two shells, stacked inside each other. If danger threatens, it can quickly assemble the two halves into a protective sphere, holding them in place with its suckers.

The new discovery comes from Julian Finn, Tom Tregenza and Mark Norman, the same terrific trio who brought us the first report of the mimic octopus's amazing shape-changing abilities. They spent over 500 hours of diving across ten years, studying the behaviour of veined octopuses in Indonesian waters.

The veined octopus has hit the headlines before for coconut-related reasons. As part of its portfolio of disguises, it will often stroll across the ocean floor on two tentacles, while wrapping the other six around its head in a tight bundle. To a passing fish, it would strongly resemble a rolling coconut.

Originally, Finn suspects that the octopuses used the empty shells of dead shellfish as defence. There's no way for an octopus to crack a coconut on its own, but it has no need to do this. Coastal human settlements often use coconuts and discard the split shells. In doing so, they have provided the veined octopus with even tougher shields.

The trio suggest that the octopus uses coconut shells as bona fide tools. Many invertebrates, such as hermit crabs, shelter in shells but they do so permanently. The octopus, however, gains no protection from its shells whatsoever when it carries them around in the stilt-walking fashion. The shells' benefits lie in the fact that they can be quickly deployed as a makeshift fortress. The fact that the octopus picks up the coconuts for later use suggests a more complicated intellect at work. As Finn writes: 

"The discovery of this octopus tiptoeing across the sea floor with its prized coconut shells suggests that even marine invertebrates engage in behaviours that we once thought the preserve of humans.

Reference: Current Biology in press