Radular tooth coating in members of Dendronotidae and Flabellinidae (Nudibranchia, Gastropoda, Mollusca)

Nudibranchs, with their mesmerizing diversity and ecological significance, play crucial roles in marine ecosystems. Central to their feeding prowess is the radula, a chitinous structure with diverse morphologies adapted to prey preferences and feeding strategies. This study focuses on elucidating wear coping mechanisms in radular teeth of carnivorous molluscs, employing Dendronotus lacteus (Dendronotidae) and Flabellina affinis (Flabellinidae) as model species. Both species forage on hydrozoans. Through scanning electron microscopy, confocal laser scanning microscopy, nanoindentation, and energy-dispersive X-ray spectroscopy, the biomechanical and compositional properties of their teeth were analysed. Results revealed distinct autofluorescence patterns and elemental compositions correlating with mechanical properties. Notably, tooth coatings, composed of calcium and silicon and high hardness and stiffness compared to the inner tooth structure, with varying mineral contents across tooth regions and ontogenetic zones, were found. The findings suggest that tooth mechanical properties are intricately linked to species ecology and function, with teeth adapted to prey type and feeding behaviors. Moreover, the presence of Ca and Si in the tooth coating highlight their role in enhancing wear resistance. Overall, this study provides valuable insights into the biomechanical adaptations of nudibranch radular teeth, shedding light on the intricate interplay between tooth structure, elemental composition, and ecological function in marine molluscs.