Main patterns of radula formation and ontogeny in Gastropoda

Abstract

Gastropoda is morphologically highly variable and broadly distributed group of mollusks. Due to the high morphological and functional diversity of the feeding apparatus gastropods follow a broad range of feeding strategies: from detritivory to highly specialized predation. The feeding apparatus includes the buccal armaments: jaw(s) and radula. The radula comprises a chitinous ribbon with teeth arranged in transverse and longitudinal rows. A unique characteristic of the radula is its continuous renewal during the entire life of a mollusk. The teeth and the membrane are continuously synthesized in the blind end of the radular sac and are shifted forward to the working zone, while the teeth harden and are mineralized on the way. Despite the similarity of the general mechanism of the radula formation in gastropods, some phylogenetically determined features can be identified in different phylogenetic lineages. These mainly concern shape, size, and number of the odontoblasts forming a single tooth. The radular morphology depends on the shape of the formation zone and the morphology of the subradular epithelium. The radula first appears at the pre‐ and posttorsional veliger stages as an invagination of the buccal epithelium of the larval anterior gut. The larval radular sac is lined with uniform undifferentiated cells. Each major phylogenetic lineage is characterized by a specific larval radula type. Thus, the docoglossan radula of Patellogastropoda is characterized by initially three and then five teeth in a transverse row. The larval rhipidoglossan radula has seven teeth in a row with differentiation into central, lateral, and marginal teeth and later is transformed into the adult radula morphology by the addition of lateral and especially marginal teeth. The taenioglossan radula of Caenogastropoda is nearly immediately formed in adult configuration with seven teeth in a row.

Morphology of the buccal apparatus of Dendronotus frondosus (Gastropoda: Nudibranchia)

“…The odontoblasts in previously studied Nudibranchia, Hygrophyla and Eupulmonata (all belonging to Euthyneura) are much larger than those described for non-Euthyneura (Vortsepneva et al, 2023).…”

“…The odontoblasts in previously studied Nudibranchia, Hygrophyla and Eupulmonata (all belonging to Euthyneura) are much larger than those described for non‐Euthyneura (Vortsepneva et al, 2023). Since the cell size often correlates with the ploidy (Rudra & Warner, 2004), one may assume that the euthyneuran odontoblasts are polyploid.…”

“…The process of radula synthesis in D. frondosus has a similar pattern to other Euthyneura, e.g., a single tooth is formed by a few cells (von Salvini‐Plawen & Steiner, 1996; Vortsepneva et al, 2023) (Table 2). However, in D. frondosus the odontoblasts of the rachidian and the lateral teeth differ in size more than tenfold.…”

“…Also, the formation zone of the radula may differ in morphology depending on the radula width. It is subdivided into two parts (outside or inside) in gastropod molluscs with broad radulae, while in those with narrow radulae, it is uniform (Vortsepneva et al, 2023).…”

Foraging on sand particles: Coatings of soft radular teeth (Paludomidae, Gastropoda, Mollusca)

“…During the intimate interaction between teeth and ingesta, the teeth become worn. Even though the radula is constantly renewed by secretion in the posterior radular region (the radular sac) by overlain and underlain epithelia (Mackenstedt & Märkel, 1987, 2001; Runham, 1963; Runham & Isarankura, 1966; Vortsepneva et al, 2021; Vortsepneva, Herbert, & Kantor, 2022; Vortsepneva, Mikhlina, & Kantor, 2022), additional mechanisms for wear reduction seem to be present. These mechanisms are well investigated in Polyplacophora and Patellogastropoda; here, very high proportions of Fe and Si are incorporated into the tooth's leading edge (i.e., the surface of the tooth that interacts directly with the ingesta; the posterior surface of the tooth facing towards the radular sac) (e.g., Barber et al, 2015; Han et al, 2011; Lu & Barber, 2012; Saunders et al, 2011; Shaw et al, 2009a, 2009b, 2010; van der Wal et al, 1999; Wang et al, 2014; Wealthall et al, 2005; Weaver et al, 2010).…”