Finite element analysis of individual taenioglossan radular teeth (Mollusca)

Abstract

Molluscs are a highly successful group of invertebrates characterised by a specialised feeding organ called the radula. The diversity of this structure is associated with distinct feeding strategies and ecological niches. However, the precise function of the radula (each tooth type and their arrangement) remains poorly understood. Here for the first time, we use a quantitative approach, Finite-Element-Analysis (FEA), to test hypotheses regarding the function of particular taenioglossan tooth types. Taenioglossan radulae are of special interest, because they are comprised of multiple teeth that are regionally distinct in their morphology. For this study we choose the freshwater gastropod species Spekia zonata, endemic to Lake Tanganyika, inhabiting and feeding on algae attached to rocks. As a member of the African paludomid species flock, the enigmatic origin and evolutionary relationships of this species has received much attention. Its chitinous radula comprises several tooth types with distinctly different shapes. We characterise the tooth's position, material properties and attachment to the radular membrane and use this data to evaluate 18 possible FEA scenarios differing in the above parameters. Our estimations of stress and strain indicate different functional loads for different teeth. We posit that the central and lateral teeth are best suitable for scratching substrate loosening ingesta, whereas the marginals are best suited for gathering food particles. Our successful approach and workflow are readily applicable to other mollusc species.