ARGONAUT, Argonauta, a genus of cephalapodous mollusca, pretty generally known by the name of paper nautilus, and, in consequence of similarity in the form of the shell, often confounded with the genus nautilus (q.v.). hut in fact much more nearly allied to the poulpe (octopus). The shell is not chambered like that of the true nautilus, but has one spiral cavity, into which the animal can entirely withdraw itself. The animal has no muscular attachment to the shell, and some naturalists therefore suspected that it might be merely, like the hermit crab, the inhabitant of a shell originally belonging to some other animal; but this question has been set at rest by the observations of Mme. Power, proving the beautiful but fragile shell to be the production of the A. itself. It has, however, also been discovered that the shell is peculiar to the female A., and does not answer the ordinary purposes of the shells of mollusca, but rather that of an " incubating and protective nest." The eggs, which are very numerous, are attached to filamentary
stalks, and by these the whole compacted mass is united to the involuted spire of the shell, where it is usually concealed by the body of the parent. The descriptions, until recently admitted into the works of the most respectable naturalists, of argonauts sailing about in pretty little fleets upon the surface of the water, employing six of their tentacula as oars, and spreading out two, which are broadly expanded for the purpose, as sails to catch the breeze, are now regarded entirely as fabulous, and indeed are founded upon an entire misapprehension of the position of the animal in its shell, and of the use of the two expanded arms or rela (sails). The membranes of these arms are extended at the pleas ure of the animal, so as to envelop the shell, and appear to be the secreting organs employed in its fabrication. Two species of A. are common in the Mediterranean.