The only existing genus of tetrabranchiate cephalopods. About four species are found living in the tropical Pacific, but many other species are found fossil. The shell is spiral, symmetrical, and chambered, or divided into several cavities by simple curved partitions, which are traversed and connected together by a continuous and nearly central tube or siphuncle. See Tetrabranchiata.
- A cephalopod mollusk of the genus Nautilus, especially N. pompilius, found in the Indian and Pacific oceans and having a spiral, pearly-lined shell with a series of air-filled chambers. Also called chambered nautilus, pearly nautilus.
- The paper nautilus.