When Jules Verne created the character of Captain Nemo in his famous novel Twenty Thousand Leagues Under the Seas of 1870, the Nautilus had only been discovered forty years before. Or rather: living specimens of this family of cephalopods had been discovered. Until then, in fact, Nautiloid shells were known exclusively in the fossil record. The Nautilus pompilius is therefore considered a "living fossil", above all for this peculiar characteristic: it is the only cephalopod currently living with an external shell. This shell, which in current specimens reaches only 20 centimeters in width, contains a series of chambers filled with gas that act as a flotation device.