Savannah: These octopuses have shells, and they're not for what you think. While the ancestors of octopuses most likely had shells, the argonaut is the only species of modern octopus that kept up that tradition. Argonauts' spiral shells mean they're often mistaken for nautiluses, and while they are distantly related, there's a few big differences between them.

Unlike nautiluses, argonauts aren't born with their shells, they grow them. At least, some do. Only female argonauts end up sporting shells. And the shells aren't attached to them, they just kinda wear it like a backpack. That's because argonauts aren't using these shells for protection. At least, not for the adult argonauts. The shell is protection for her eggs.

See, argonauts don't live on a den on the seafloor like most other octopuses do; they're always on the go. So the argonauts' shells let them safely bring their eggs everywhere they go, which is why -

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