3D model radula of Gastropteron rubrum

The molluscan feeding structure is the radula, a chitinous membrane with
teeth, which are highly adapted to the food and the substrate to which the
food is attached. In Polyplacophora and Patellogastropoda, the handling of
hard ingesta can be facilitated by high content of chemical compounds
containing Fe or Si in the tooth cusps. Other taxa, however, possess teeth
that are less mineralized, even though animals have to avoid structural
failure or high wear during feeding as well. Here, we investigated the
gastropod Gastropteron rubrum, feeding on hard Foraminifera, diatoms and
Porifera. Tooth morphologies and wear were documented by scanning electron
microscopy and their mechanical properties were tested by nanoindentation.
We determined, that gradients of hard- and stiffness run along each tooth,
decreasing from cusp to basis. We also found, that inner lateral teeth are
harder and stiffer than the outer ones. These findings allowed us to
propose hypotheses about the radula-ingesta interaction. In search for the
origins of the gradients, teeth were visualized using confocal laser
scanning microscopy, to determine the degree of tanning, and analyzed with
energy-dispersive X-ray spectroscopy, to test the elemental composition.
We found that the mechanical gradients do not have their origins in the
elemental content, as the teeth did not contain high proportions of metals
or other minerals, which indicates that their origin might in the degree
of tanning. However, in the tooth surfaces, which interact with the
ingesta, high Si and Ca content was determined, which is likely an
adaptation to reduce wear.