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| SECTION OF NAUTILUS |
Nautilus (na̤′tĭ-lŭs), a mollusk having a chambered shell and belonging to the class Cephalopoda. It is the sole living representative of one order of that class, possessing four gills, while the other cephalopods have only two. Its shell is not uncommon on the shores of warm seas, but the animal is not often found inhabiting the shell. It creeps about the bottom, and the floating shell is the result of storms. It is called both pearly nautilus and chambered nautilus. The former name comes from the pearly appearance of the innermost layer of the shell, the latter from the circumstance that the spiral shell is divided into a set of chambers. The animal lives in the outermost one. When very young, it lives in a small shell shaped like a horn. As it grows, it draws the body forward, secretes a pearly partition just back of it, and adds to the margin of the opening of the shell; this is repeated, and a set of chambers results. The animal has a plump body connected with the apex of the shell by a sort of cord, which passes through the center of each partition wall. There are large eyes. The head is surrounded by a number of arms or tentacles, which do not possess suckers like the squid or devilfish, to which the nautilus is related. The paper nautilus or argonaut is sometimes confused with the true nautilus. It, however, belongs to another division of the cephalopods, having only two gills. The shell of this animal is secreted by the female only, as a case or cradle for the eggs, and is not a shell to protect the animal. In geological times there were huge chambered shells inhabited by animals like the nautilus. These shells were straight instead of being coiled, and are well known under the name orthoceratites. See Woodward's Manual of the Mollusca and Holmes' poem of The Chambered Nautilus.