Nautilus is one of two remaining genera included in the cephalopod family Nautilidae, which is included in the superfamily Nautilaceae. The other genus being Allonautilus.
Nautilus, as with all nautiloids, has an external shell, one that is involutely coiled so that the final whorl completely overlaps the previous whorls. The shell, as with all externally shelled cephalopods, is divided into a chambered phragmocone through which runs the siphuncle, and a living or body chamber which houses the animal while alive. Instead of arms, and possibly tentacles, with suckers or hooks, as with coleoids, nautiluses have some 90 or so sticky finger-tentacles that can be withdrawn into fleshy sheaths, or protracted. Their eyes are open to the sea, lack a cornia, are like a simple pin-hole camera. The whorl section is ovoid in contrast to that of Allonautilus which is quadrate. The umbilicas is small to moderate, about 5 to 16 percent of the diameter of the shell. That of Allonautilus is larger, about 20 percent of the shell diameter.
Nautilus is found in the western tropical Indo-Pacific, from Indonesia east to American Samoa and from Northern Australia north to the Philippines. They spend their time near the sea floor, off and below coral reefs at depths of around 500 meters during the day and ascend to shallower depths to hunt during the night. They move by "jet propulsion", by forcing water from within the mantle cavity through a tube called a hyponome, which can be directed.
References[]
Chambered Nautiluses FAO Species Catalogue for Fishery Puroises No. 4, Vol, 1 [1]
Nautilus classification in Animal Diversity Web [2]
Chambered Nautiluses, Nautilus pompilius [3]