By Susan Milius
After centuries of speculation, biologists have documented one way a strange group of octopuslike creatures use their seashell-shaped cases.
Female argonauts, a group of four species that are close cousins of octopuses, grow delicate white shell-like cases. Biologists have found argonauts with air bubbles in their cases, and now it turns out the animals use the trapped air to float at a comfortable depth, says Julian Finn of Museum Victoria in Melbourne, Australia.
In the first reports from scuba observations of wild argonauts, Finn maneuvered Argonauta argo females so air escaped from their cases. The animals flailed as if struggling to maintain their orientation and quickly jetted to the water surface.