Nautilus Shell Architecture

Abstract

The familiar shape of the shell of Nautilus pompilius has been described thoroughly (e.g., Stenzel, 1964) and needs little introduction. We wish to consider to what extent the shell's design resists water pressures as great as 8.34 megapascals (MPa) [830 m depth equivalent (Kanie and Hattori, 1983)]. The loading of the last septum and phragmocone wall is due to the difference in pressure between the partial vacuum within the gas chambers (<1 atm) and the ambient hydrostatic head of seawater. The strength and stiffness of the aragonite shell permit it to act as a constant-volume hydrostatic apparatus that enables Nautilus to maintain neutral buoyancy. The gas diffuses into the chambers via the siphuncular tube as the cameral water is removed from behind the recently completed last septum of the growing shell. Because the equilibrium gas pressures in the ocean are largely independent of water depth, there is no difference in the final gas pressure of chambers grown at different depths.