ИСТИНА

The radula, comprising a chitinous membrane with teeth arranged in longitudinal and transverse rows, is a characteristic element of the feeding apparatus within the Mollusca. Radular morphology is particularly diverse in gastropods, in which it has been studied in detail and found to be a source of traditionally important taxonomic characters. Rhipidoglossan radula, which is characterized by presence of a central tooth, several lateral teeth, and numerous long marginal teeth in each transverse row, is found in three different subclasses – Vetigastropoda, Neritomorpha and “lower” Heterobranchia. Details of radula formation and its ultrastructure have not to date been studied in any species with a rhipidoglossan radula. Herein we present the data of complex studies of the radular fine morphology and radular formation in two vetigastropod species (Puncturella noachina and Margarites helicinus), and one species of Neritimorpha (Nerita litterata). The radula itself and the radular formation zone were studied using light and electron microscopy (scanning and transmission), as well as confocal laser scanning microscopy. The major peculiarity of Vetigastropoda rhipidoglossan radular formation is posterior bifurcation of the radular formation zone, creating paired horns into which the odontoblasts of marginal teeth extend. Significant morphological difference in the formation of the radula between Nerita litterata and two studied vetigastropod species is the absence of external division of the blind end of the radular sac. Nevertheless division of the formation zone in N. litterata into two partitions can be seen on histological sections. The marginal teeth of N.litterata are synthesized in these horns as well as in vetigastropod species. The adaptive features of the formation zone of rhipodoglossan radula relate to the increase in the secreting surface for the formation of very long and numerous marginal teeth of a wide radula. Keywords: ultrastructure, odontoblast, radular formation zone Acknowledgments: This research was carried out as a part of the Scientific Project of the State Order of the Government of the Russian Federation to Lomonosov Moscow State University, No 121032300121-0. Support was provided by the Russian Science Foundation No 21-14-00042.