Diversity of Mineral Systems, Material Compositions and Mechanical Properties in Molluscan Radulae

The radula, composed on a chitinous membrane with longitudinal and transversal rows of embedded teeth, is the molluscan autapomorphy for food gathering and processing. Within the Mollusca, this organ is highly diverse in morphology, material composition, and its mechanical properties. We here provide a summary of the known material composition and properties of radular teeth and their relationship with the preferred ingesta, the tooth function and the resistance of structures to failure and wear. In general, multiple mechanisms, e.g. the chemical composition, the micro- and nanostructure of teeth, the underlying supporting structures, or the interplay between structures, contribute to the radular performance. In different molluscan taxa, these mechanisms contribute to different extents to both wear- and failure-reduction (i.e., some teeth possess high contents of metals and minerals whereas, in other taxa, teeth are stiffened and hardened by the degree of cross-linking). This highlights the potential of evolving convergent solutions to common biomechanical constrains at the ingesta processing apparatus.