Mechanical properties, degree of sclerotisation and elemental composition of the gastric mill in the red swamp crayfish Procambarus clarkii (Decapoda, Crustacea)

Abstract

The gastric mill of Decapoda is a unique feature consisting of interacting teeth, stabilizing ossicles, and particle sorting setae. As this organ is involved in the mechanical fragmentation of the food, it serves as interface between organism and environment. There is an ongoing debate to which extend structures are shaped due to phylogeny or to ecology. As material properties complement morphology and hold information about functionality and trophic preferences, we here aim at providing a basis for more intensely comparative research on material composition and properties of gastric mill components. Data on the micro-structure, documented via scanning electron microscopy (SEM), on the elemental composition, determined by energy-dispersive X-ray spectroscopy (EDX, EDS), on the heterogeneities in material properties, visualized by confocal laser scanning microscopy (CLSM), and on the mechanical properties hardness and elasticity (i.e., Young’s modulus), tested by nanoindentation technique, of gastric mill components from the red swamp crayfish Procambarus clarkia is here presented. The elemental composition of gastric mill components was studied previously in other taxa, but the mechanical properties were never tested before. As epicuticle and exocuticle could be analyzed individually, due to rather large thickness of the epicuticle, material property gradients, with values decreasing from the interacting surface towards interior, could be determined. Finally, we were able to relate the mechanical property data and the autofluorescence signals with the elemental composition and the degree of tanning.

Coping with abrasive food: diverging composition of radular teeth in two Porifera-consuming nudibranch species (Mollusca, Gastropoda)

“…We therefore propose that the inorganic content of the tooth tips influences the emitted autofluorescence signal. This is similar to the crustacean exoskeletons, where Ca was found to cause a blue signal and Si a green signal [125][126][127].…”

“…the inner structure (figure 3a, right side). This is the usual situation (see [42,43,48,52,53,101,127]). We here searched for teeth that had basis, stylus and tip on display, and tested at these three localities to receive data on mechanical property gradients within each tooth (figure 3b).…”

“…Two radulae per species, which were previously documented via SEM, were detached from carbon tape by alcohol, cleaned with an ultrasonic bath, and attached to glass object slides by double-sided adhesive tape, following our previous protocol [52,74,96,101,127,139]. Then, each radula was surrounded by a small metallic ring.…”

“…To test the mechanical properties, nanoindentation was performed on two additional radulae per species (for detailed protocol see [42,43,48,52,53,101,127]). Similar to the radulae used for EDX, the radulae were arranged on glass object slides, surrounded by a small metallic ring.…”

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

“…Abrasive particles, either as part of the animal's natural diet (e.g., phytoliths) or part of the ingesta (e.g., sand particles) are challenging for mouthparts, because they cause wear and may consequently add to functional deterioration of, for example, the radula. Adaptations to reduce particle-induced wear may include thick enamel caps, hypsodonty, or specific traits in the enamel ultrastructure in the teeth of mammals (e.g., Hummel et al, 2010;Preuschoft, 2022;Ungar, 2015;Winkler et al, 2022), or high proportions of Si and Ca in the gastric mill teeth of decapod crustaceans (Krings, Brütt, & Gorb, 2022d;Nesbit & Roer, 2016;Vatcher et al, 2015). In polyplacophoran or patellogastropod species, high proportions of Fe, Si, and Ca are incorporated in the dominant tooth's leading edge (the posterior tooth surface facing towards the radular sac) as mechanical adaptation to foraging on harder substrates (for reviews, see Brooker & Shaw, 2012;Joester & Brooker, 2016).…”