Feeding experiments on Vittina turrita (Mollusca, Gastropoda, Neritidae) reveal tooth contact areas and bent radular shape during foraging

Abstract

The radula is the food gathering and processing structure and one important autapomorphy of the Mollusca. It is composed of a chitinous membrane with small, embedded teeth representing the interface between the organism and its ingesta. In the past, various approaches aimed at connecting the tooth morphologies, which can be highly distinct even within single radulae, to their functionality. However, conclusions from the literature were mainly drawn from analyzing mounted radulae, even though the configuration of the radula during foraging is not necessarily the same as in mounted specimens. Thus, the truly interacting radular parts and teeth, including 3D architecture of this complex structure during foraging were not previously determined. Here we present an experimental approach on individuals of Vittina turrita (Neritidae, Gastropoda), which were fed with algae paste attached to different sandpaper types. By comparing these radulae to radulae from control group, sandpaper-induced tooth wear patterns were identified and both area and volume loss could be quantified. In addition to the exact contact area of each tooth, conclusions about the 3D position of teeth and radular bending during feeding motion could be drawn. Furthermore, hypotheses about specific tooth functions could be put forward. These feeding experiments under controlled conditions were introduced for stylommatophoran gastropods with isodont radulae and are now applied to heterodont and complex radulae, which may provide a good basis for future studies on radula functional morphology.

From the knitting shop: the first physical and dynamic model of the taenioglossan radula (Mollusca: Gastropoda) aids in unravelling functional principles of the radular morphology

“…For example, the direct inference simply from tooth shape [32], e.g. interpreting from a broad cusp directly its ability to loosen food items, is far too speculative, especially since experimental approaches revealed that not all teeth necessarily interact with the substrate [33], but still contribute to the overall radular function by, for example, reinforcing the spanned radula [34].…”

“…Second, the configuration of the radula during foraging is not the same as that of mounted radula [34]: molluscs are capable of bending, twisting and flapping their radula, as previously documented by studying foraging gastropods through glass surfaces [35][36][37][38][39][40][41][42] and/or by analysing feeding tracks [13,35,36,39,[43][44][45][46][47][48][49][50]. However, feeding tracks are difficult to interpret and additionally, only teeth, which were pressed into the substrate forcefully, rather leave a mark and teeth that do not interact or interact with the low force do not leave tracks [34]. Experiments, making interaction of teeth with substrate clearly visible, are without doubts highly desired, as the knowledge about precise contact areas of teeth could further contribute to determining tooth functionality, because these areas function as load-transmitting regions.…”

“…Experiments, making interaction of teeth with substrate clearly visible, are without doubts highly desired, as the knowledge about precise contact areas of teeth could further contribute to determining tooth functionality, because these areas function as load-transmitting regions. Unfortunately, such a designation is rather limited to feeding experiments involving the analysis of tooth wear, induced by sandpaper [33,34], due to three reasons. (i) Foraging can only be documented on rather large gastropods (obtaining sharp videos of fast moving, very small structures maybe from small, fast feeding and moving gastropods is almost impossible).…”

“…In addition to this 'collective effect' of teeth, experiments on wear, induced by abrasive sandpaper, revealed that more mechanisms preventing the structural failure of the radula seem to be present [33,34]. The radular supporting structures (buccal mass muscles with underlain odontophoral cartilages) were assumed as contributors for failure prevention and as main radular components enabling its proper functioning.…”

Finite Element Analysis Relating Shape, Material Properties, and Dimensions of Taenioglossan Radular Teeth with Trophic Specialisations in Paludomidae (Gastropoda)

“…Summary of the preferred feeding substrate with the references, the previously assigned feedings substrate category (mixed, solid, and soft; from Krings et al,Krings, 2021), and previously determined Young's moduli (GPa) of the distinct tooth parts (with collection number and quantity of analysed specimens, and analysed tooth parts (data fromKrings et al, 2019, 2021b are provided for each species studied. Geometrical variables of radulae (widt and volume of the model) necessary to determine the nominal force for each species.…”