Perfect Argonaut Shell

Found on a Costa Rican beach today. Female Argonaut Octopuses create their own shells by secreting a calcite substance from two elongated tentacles, like a pair of 3D-printers.

“What’s interesting about the argonaut is that its ancestors long ago evolved away the shell, then later on evolved an entirely new way of constructing it and an entirely new use for it as a reproductive aid. Still, though, it arrived at the same solution to the buoyancy problem that the early cephalopods solved with their own shells, which just goes to show what an endlessly creative force evolution is.” — WIRED