Foraging on sand particles: Coatings of soft radular teeth (Paludomidae, Gastropoda, Mollusca)

The radula is the ingesta-gathering structure in Mollusca. As interface, it has to perform various tasks without functional deterioration caused by wear. Wear prevention is well investigated in mollusks that forage on rocks and that generate high punctual pressure with their hard teeth, which contain high inorganic contents at their tips. In mollusks that forage on softer substrate, such as sand surfaces, and have relatively soft teeth, wear prevention has not been a focus of study before. Here, we studied the teeth of Limnotrochus thomsoni, which are used for raking algae from sand. For comparison, we investigated the soft outer teeth of Lavigeria grandis, which are used in gathering particles after the ingesta is loosed from the rock surface. SEM revealed scratches on all surfaces of the teeth and suggests that every tooth side interacts with abrasive particles during foraging. Analysis of stomach content revealed that sand particles of 10–20 μm diameter are ingested. By EDX/EDS, we studied the composition of the teeth and determined that high proportions of Ca are present on all surfaces, which could be an adaptation to reduce abrasion. Finally, we here present evidence for the existence of a canal within the teeth, which could potentially serve as delivery pathway of minerals during tooth maturation and has not been previously detected in Gastropoda.