May 20, 2010 : Argonaut

Argonaut

The argonauts (genus Argonauta, the only extant genus in the Argonautidae family) are a group of pelagic octopuses. They are also called paper nautiluses, referring to the paper-thin shell that females secrete. This structure lacks the gas-filled chambers present in chambered nautilus shells and is not an inherited cephalopod shell, but rather an evolutionary innovation unique to the genus Argonauta. It is used as an eggcase and for trapped surface air to maintain buoyancy.

Video source here at Discover Magazine.