Wear reduction
Wear reducing mechanisms are well-investigated in Polyplacophora and Patellogastropoda. Here, high proportion of Fe and Si are incorporated into a thick leading edge (surface layer), which is hard and protected against wear (Kirschvink & Lowenstam, 1979; Kim et al., 1989; Lowenstam & Weiner, 1989; van der Wal, 1989; van der Wal et al., 1999; Brooker et al., 2003; Lee et al., 2003a, 2003b; Saunders et al., 2009, 2011; Weaver et al., 2010; Wang et al., 2013; Kisailus & Nemoto, 2018; Krings et al., 2022c). Compared to the harder outer edge, the teeth possess a softer inner structure, which reduces crack formation (van der Wal, 1989; van der Wal et al., 1999; Grunenfelder et al., 2014). In some paludomid and nudibranch taxa, we previously also identified an outer layer with high Si or Ca content on the tooth region, which interacts with the food (Krings et al., 2022a, 2023; Krings & Gorb, 2023a). This layer, however, was very thin in comparison with that of the chitons and limpets, rendering these teeth as lightweight structures. InGastropteron rubrum , we detected high content of Si and Ca in the tooth regions, which interact with the ingesta. This suggests that this also reduces wear during feeding. A similar adaptation involving the incorporation of Si at the tooth tip and the presence of a soft tooth base to reduce wear by foraging on hard prey, such as diatoms, has also been found in the gnathobases of Copepoda (Michels et al., 2012).