The evolution of the radula in molluscs: what was first, flexoglossy or stereoglossy?

Vortsepneva, E.V.; Mikhlina, A.L.; Kantor, Y.I.

Авторы: Vortsepneva E.V., Mikhlina A.L., Kantor Yu I.
Журнал: Зоология беспозвоночных
Том: 22
Номер: 1
Год издания: 2025
Издательство: Товарищество науч. изд. КМК
Местоположение издательства: М.
Первая страница: 202
Последняя страница: 218
DOI: 10.15298/invertzool.22.1.13
Аннотация: Two fundamental types of radulae in Mollusca have been recognized: stereo-glossate and flexoglossate. The former is characterized by a fixed connection between theteeth and the radular membrane, a membrane that is not folded longitudinally, and parallelfeeding tracks where the teeth act as a rasp. This type of radula has been considered presentin Monoplacophora, Polyplacophora, Scaphopoda, and one gastropod subclass, the Patello-gastropoda, and is therefore thought to represent the ancestral state of radulae in Gastropoda.In contrast, the flexoglossate radula is characterized by a mobile connection between theteeth and the radular membrane, longitudinal folding of the membrane within the radularsac, and the mobility of rotating marginal teeth, which follow different trajectories duringfeeding. The flexoglossate radula is typical of all Gastropoda except Patellogastropoda.A detailed examination of the radular apparatus of ten gastropod species from differentsubclasses, including Patellogastropoda, as well as three Polyplacophora species, has al-lowed us to reevaluate the stereoglossate condition in gastropods and polyplacophorans.We demonstrate that the radular membrane is folded longitudinally in the radular sac inall the species studied. Among Patellogastropoda, this was most obvious in Scutellastralongicosta, which has a broader and more complete radular transverse row (13 teeth),though traces of folding were observed even in Testudinalia testudinalis, which has only 4teeth in a transverse row. Similarly, the radular membrane was folded longitudinally in theradular sac of chitons, which were previously thought to have a stereoglossate radular type.Our data allowed us to re-evaluate the established views on the evolution of radula. Mostlikely, the plesiomorphic state of molluscan radula is a flexible flexoglossate condition. Weconclude that the stereoglossate condition in Patellogastropoda is not a distinct radular typebut rather a secondary modification of an originally flexoglossate radula. This modificationis related to the reduction of teeth in the transverse row, retaining only the central portionof the radula, consisting of two pairs of lateral teeth.
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The evolution of the radula in molluscs: what was first, flexoglossy or stereoglossy?статья

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