bogleech:dynamicoceans:The paper nautiluses, Argonauta sp., are not nautiluses at all, they are octo
bogleech:dynamicoceans: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.Source Video ImageWhat’s really amazing is how the shell looks SO MUCH like that of a Nautilus, even though it doesn’t grow as a part of the body like a true shell. It’s produced an entirely different way and there wouldn’t actually be any point at which one derived from the other in their evolution.The shape is similar either by convergence, which is likely, or according to some hypotheses, because these animals may have once borrowed the shells of nautiloids back when such animals dominated the oceans. The paper could have begun as a lining for the borrowed home and continued to be useful even after most of the shelled cephalopods died out. -- source link
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