Nautilus, plural nautiluses, or nautili, either of two genera of cephalopod mollusks: the pearly, or chambered, nautilus (Nautilus), to which the name properly applies; and the paper nautilus (Argonauta), a cosmopolitan genus related to the octopus.

nautilus Nautilus (Nautilus belauensis). Lee R. Berger

Read More on This Topic cephalopod squid, cuttlefish, and chambered nautilus are familiar representatives. The extinct forms outnumber the living, the class having attained...

The pearly nautilus has a smooth, coiled external shell about 25 cm (10 inches) in diameter, consisting of about 36 separate chambers, the outermost of which it lives in. The chambers are connected by a tube (the siphuncle) that adjusts the gases in the chambers, allowing the shell to act as a float and maintain neutral buoyancy. Nautilus swims about the ocean using jet propulsion, searching for shrimp or other prey. It uses up to 94 small, suckerless, contractile tentacles for capturing prey. The animals live at depths of 50 to 600 metres (about 160 to 1,970 feet). Nautilus, the last surviving genus of the ancient order Nautiloidea, is important in paleontology for dating the strata in which it appears.

chambered nautilus Chambered nautilus (Nautilus pompilius). © rodho/Shutterstock.com