Finite Element Analysis Relating Shape, Material Properties, and Dimensions of Taenioglossan Radular Teeth with Trophic Specialisations in Paludomidae (Gastropoda)

Abstract

The radula, a chitinous membrane with embedded tooth rows, is the molluscan autapomorphy for feeding. The morphologies, arrangements and mechanical properties of teeth can vary between taxa, which is usually interpreted as adaptation to food. In previous studies, we proposed about trophic and other functional specialisations in taenioglossan radulae from species of African paludomid gastropods. These were based on the analysis of shape, material properties, force-resistance, and the mechanical behaviour of teeth, when interacting with an obstacle, which was previously simulated for one species (Spekia) by the finite-element-analysis (FEA) and, for more species, observed in experiments. In the here presented work, we test the previous hypotheses by applying the FEA on 3D modelled radulae, with incorporated material properties, from three additional paludomid species. These species forage either on algae attached to rocks (Lavigeria), covering sand (Cleopatra), or attached to plant surface and covering sand (Bridouxia). Since the analysed radulae vary greatly in their size between species, we additionally aimed at relating the simulated stress and strain distributions with the tooth sizes by altering the force/volume. For this purpose, we also included Spekia again in the present study. Our FEA results show that smaller radulae are more affected by stress and strain than larger ones, when each tooth is loaded with the same force. However, the results are not fully in congruence with results from the previous breaking stress experiments, indicating that besides the parameter size, more mechanisms leading to reduced stress/strain must be present in radulae.

Coping with abrasive food: diverging composition of radular teeth in two Porifera-consuming nudibranch species (Mollusca, Gastropoda)

“…For this species, thin leading edges containing high levels of calcium and silicon were found to be responsible for abrasion reduction, while the inner structure (core) of the teeth, in contrast, was not highly mineralized. These results, in combination with the previous studies on the paludomid radular teeth [48][49][50][51][52][53]61,63,80], suggests that wear and failure prevention can be achieved without the incorporation of high proportions of minerals or metals, rendering teeth of L. grandis as an example for a highly functional organic composite.…”

“…During this bending motion, teeth of F. picta and D. pseudoargus probably interact with the neighbouring teeth. Such interaction was previously documented for other gastropod species (see [54][55][56][57][58][59]102]), simulated by finite-element analyses [49,51], observed during breaking stress experiments [50,63] and/or in a physical radular model [61]. Such interaction reduces structural failure, because it enables teeth to rely on teeth of adjacent tooth rows and to redistribute the contact stresses.…”

“…(e.g. [49][50][51]61,63,[97][98][99][100][101][102][103]). This is reflected by the tooth's regional mechanical properties, because they contribute to the overall mechanics of structures.…”

“…hardness and Young's modulus) and their gradients need to be tested, as they contribute to the understanding of overall functionality of the structure (e.g. [24,26,27,[42][43][44][45][46][47][48][49][50][51][52][53]). Part of radular function is the reduction of structural failure or high degrees of wear during feeding.…”

“…(1) In some species, neighbouring teeth can interlock when loaded, leading to stress redistribution, when in contact with the substrate. This mechanical behaviour depends on the arrangement and geometry of teeth [26,[54][55][56][57][58][59][60][61][62], material properties [42,48,49,51,53] and the water content [50,63]. (2) The radula consists of chitin fibres with associated proteins [64], which form a fibrous composite organic matrix [65].…”