Development of the Embryonic Shell of Nautilus

The organization of this chapter follows the development of the shell of Nautilus from the formation of the cicatrix through hatching. The description of the cicatrix is based mainly on study of one embryo of N. belauensis in early organogenesis, in which periostracum and crystals of aragonite were just beginning to form (Arnold and Carlson, 1986). Development through the one-chambered stage is based largely on a second embryo of N. belauensis, in which the first chamber was in the process of forming, but a calcified septum had not yet developed (Arnold and Carlson, 1986).