Vortsepneva E.V. 2020. Radula morphology of Clione limacina (Phipps, 1774) (Gastropoda: Heterobranchia: Gymnosomata) // Invertebrate Zoology. Vol.17. No.3: 291–309 [in English].
Department of Invertebrate Zoology, Biological faculty, Moscow State University, Leninskie gory 1/12, 119234 Moscow, Russia. E–mail: vortcepneva@gmail.com
doi: 10.15298/invertzool.17.3.06
ABSTRACT: The radula of gastropods is a unique structure of the feeding apparatus, which is characterized by its incredible morphological diversity. The radula consists of the teeth attached to the radular membrane and is formed by specialized cells in the radular sac. The mode of the radula formation, including the type of secretion, the number, size, and shape of the cells forming one tooth, can vary significantly between different mollusks. Clarification of this diversity is the key to determining the patterns of radula formation in Gastropoda. The general morphology and ultrastructure of radula of Clione limacina (Gastropoda: Pteropoda) was studied using light, electron, and confocal laser scanning microscopy for the first time. The radula formula is n–1–n with wide central tooth and hook-like lateral teeth (from 7 to 12). The unique feature for the Gymnosomata is the increasing size and number of teeth during the life of the animal, possibly, due to the unique position of odontoblasts, located on the periphery of the blind end of the radular sac. The ultrastructure of C. limacina combines features and characteristics that are typical for all Heterobranchia. Ultrastructure of the formation zone (cells in the formation zone with poor differentiation), structure of radular membrane, and absence of subradular membrane are characteristic for C. limacina. The mode of tooth formation (one tooth is formed by several odontoblasts and microvillar secretion), radular bolsters, and muscular morphology are similar to other Heterobranchia. The firm connection between radula and radular bolster without a subradular membrane, the muscular radular support structure, which gives additional mobility to the radula, and muscles which connect hook sacs could indicate a significant contribution of the radula to scraping the prey. As a result of this study, the ultrastructure of the radular apparatus of one species Gymnosomata was described for the first time. These data significantly extend our knowledge of the gastropod’s radula formation.
KEY WORDS: ultrastructure, chitin, radular formation, odontoblasts, Pteropoda.