Cited research: Proc. R. Soc. B doi:10.1098/rspb.2010.0155 (2010)

Female argonaut octopuses produce and inhabit brittle 'paper nautilus' shells in which they store their eggs. Scientists have speculated that the shells also help to keep the creatures buoyant. Julian Finn and Mark Norman at Museum Victoria in Melbourne, Australia, confirm that the air sometimes seen trapped in these creatures' shells is used for this purpose.

The researchers captured three females of the species Argonauta argo (pictured) and removed all trapped air from their shells. After release in the ocean, the argonauts jetted towards the surface, where they forced their shells above water and collected air. They then sealed this air into their shells using a pair of arms and forced themselves downwards to a depth at which they became neutrally buoyant. D.P.C.

Credit: J. FINN, MUSEUM VICTORIA