The paper nautiluses, Argonauta sp., are not nautiluses at all, they are octopuses! The paper thin white calcareous ‘shell’ is actually an egg case made by females.
The shell is made of a thin calcite the female secretes as she matures. It also functions as a swimming aid, females use the shell to ‘gulp’ a measured volume of air at the sea surface, seal off the captured gas using flanged arms and forcefully dive to a depth where the compressed gas buoyancy counteracts body weight. When scientists removed the air from the octopuses’ shells underwater, the octopuses tended to sink before swimming to the surface, taking in more air and then jetting back down to where they were weightless.
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