Nautilus

Nautilus is a genus of marine cephalopods in the family Nautilidae, a living-fossil lineage whose oldest known fossils date to the Late Eocene. It sits within the order Nautilida, class Cephalopoda, and currently comprises seven living species, including the type species Nautilus pompilius, the most widespread of the group, along with N. macromphalus, N. stenomphalus, N. belauensis, and three species formally described only in 2023, N. samoaensis, N. vanuatuensis, and N. vitiensis. Nautilus differs from its sister genus Allonautilus in several respects, including sensory organs: its eyes lack lenses or corneas and move on muscular stalks, and it bears chemosensory rhinophores and tentacles with a variety of receptor functions, all housed in a chambered aragonite shell with a simple internal wall structure that distinguishes it from the extinct ammonites. The whole family Nautilidae is listed under CITES Appendix II because of population declines driven by overfishing.