The rhipidoglossan radula: Radular morphology and formation in Nerita litterata Gmelin, 1791 (Neritimorpha, Neritidae).

The rhipidoglossan radula, consisting of numerous teeth in each transverse row, is characteristic of phylogenetically distant groups of gastropods, including Vetigastropoda, Neritimorpha and 'lower' Heterobranchia. Previous studies have revealed the main patterns in the formation of the rhipidoglossan radula of vetigastropods, the main feature of which is the division of the formation zone into two horns, where marginal teeth are formed by a multilayered epithelium (odontoblasts). This work is devoted to the study of the formation of the rhipidoglossan radula of Nerita litterata using light and electron microscopy. The data obtained show that, despite the different external morphology of the radular sac of neritids and vetigastropods, the radular sac of N. litterata, like that of vetigastropods, is divided into two parts, in which the marginal teeth are similarly formed by odontoblasts located in more than one layer. It seems probable that this complex, three-dimensional structure of the formation zone is associated with a broad radula with numerous elongate marginal teeth and could be characteristic of other gastropods with this type of radula. Additional supporting rods located along the odontoblasts and consisting of vacuolated cells were first discovered in Nerita.