Shelling out





At last we know why female argonaut octopuses have a shell, and what use they put them to. Previously, scientists thought the females used them to keep their delicate eggs safe. Now, by capturing argonauts and releasing them at different depths, Julian Finn and Mark Norman of Museum Victoria in Melbourne, Australia, have established that they use the shells to capture and compress air for buoyancy control. In this picture the octopus has headed to the surface to scoop in some air with her shell.



Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2010.0155



(Image: Julian Finn/Museum Victoria)