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. (Zoöl.) 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.
&fist; 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 imagined.
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.
