This octopus makes its “shell” with its arms

Argonaut seems to carry a small white spiral shell, so thin that it is sometimes called paper nautilus. The animal is an octopus. Its envelope does not come from the mantle, like a classic mollusk shell: it is produced by the tissues of its arms.

Only females build this structure of calcium carbonate, which is used to protect eggs. It also contributes to their buoyancy. Argonauts can take air to the surface and then descend; compression of that air helps to compensate for the weight of their body.

The ancient idea that these animals borrowed a shell from other species turned out to be wrong. The resemblance had made one imagine a property that was not theirs. What was taken for a recovered housing is therefore a personal construction, both room for young people and accessory suspension in the water.