Nautilina in the context of Centroceratina

A nautilus (from Latin nautilus 'sails like a vessel'; from Ancient Greek ναυτίλος (nautílos) 'seaman, sailor') is any of the various species within the cephalopod family Nautilidae. This is the sole extant family of the infraorder Nautilaceae and the suborder Nautilina.

It comprises nine living species in two genera, the type of which is the genus Nautilus. Though it more specifically refers to the species Nautilus pompilius, the name chambered nautilus is also used for any of the Nautilidae. All are protected under CITES Appendix II. Depending on species, adult shell diameter is between 10 and 25 cm (4 and 10 inches).

The Nautilaceae form one of five superfamilies that make up the Nautilida according to Bernard Kummel (1964), and the only one that survived past the Triassic. The Nautilaceae comprise six families: Nautilidae, Paracenoceratidae, Pseudonautilidae, Cymatoceratidae, Hercoglossidae, and Aturiidae. Shimanskiy (1957) separated the Paracenoceratidae and Pseudonautilidae from his near equivalent Nautilina and added them to the Lyroceratina, expanding the equivalent Clydonautiloidea and bringing it into the Jurassic. The Nautilaceae are represented by Nautilus and Allonautilus genera of the Nautilidae, the only extant family in this group.

Species in the Nautilaceae are generally smooth and involute with straight to strongly sinuous sutures and a small siphuncle. Some groups have sinuous plications or ribs.