The Collaborative International Dictionary of English v.0.48:
Nautilus \Nau"ti*lus\, n.; pl. E. Nautiluses, L. Nautili.
[L., fr. Gr. nayti`los a seaman, sailor, a kind of shellfish
which was supposed to be furnished with a membrane which
served as a sail; fr. nay^s ship. See Nave of a church.]
1. (Zool.) 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
Note: The head of the animal bears numerous simple tapered
arms, or tentacles, arranged in groups, but not
furnished with suckers. The siphon, unlike, that of
ordinary cephalopods, is not a closed tube, and is not
used as a locomotive organ, but merely serves to
conduct water to and from the gill cavity, which
contains two pairs of gills. The animal occupies only
the outer chamber of the shell; the others are filled
with gas. It creeps over the bottom of the sea, not
coming to the surface to swim or sail, as was formerly
2. The argonaut; -- also called paper nautilus. See
Argonauta, and Paper nautilus, under Paper.
3. A variety of diving bell, the lateral as well as vertical
motions of which are controlled, by the occupants.