Elemental analyses reveal distinct mineralization patterns in radular teeth of various molluscan taxa

Abstract

The molluscan phylum is the second specious animal group with its taxa feeding on a variety of food sources. This is enabled by the radula, a chitinous membrane with embedded teeth, one important autapomorphy. Between species, radulae can vary in their morphology, mechanical, and chemical properties. With regard to chemical composition, some taxa (Polyplacophora and Patellogastropoda) were studied extensively in the past decades, due to their specificity to incorporate high proportions of iron, calcium, and silicon. There is, however, a huge lack of knowledge about radular composition in other taxa. The work presented aims at shedding light on the chemistry by performing energy-dispersive X-ray spectroscopy analyses on 24 molluscan species, thereof two Polyplacophora, two Cephalopoda, and 20 Gastropoda, which was never done before in such a comprehensiveness. The elements and their proportions were documented for 1448 individual, mature teeth and hypotheses about potential biomineralization types were proposed. The presented work additionally comprises a detailed record on past studies about the chemical composition of molluscan teeth, which is an important basis for further investigation of the radular chemistry. The found disparity in elements detected, in their distribution and proportions highlights the diversity of evolutionary solutions, as it depicts multiple biomineralization types present within Mollusca.

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

“…It was previously determined, that Na, K, and S can be related to the protein bonding and degree of tanning [e.g., 92 – 94 ] —potentially this is also the case in crustaceans. The detected proportions of Fe and Zn potentially also increase the stiffness and hardness in the gastric mill, comparable to molluscan teeth—even though, the detected proportions are very small in comparison to the incorporations in Polyplacophora and limpets [e.g., 58 , 60 , 95 , 96 ]. But this again awaits further investigations.…”

Material gradients in gastropod radulae and their biomechanical significance: a combined approach on the paludomid Lavigeria grandis

“…For the paludomid gastropod Lavigeria grandis, we previously examined the nanostructure of the material by scanning electron microscopy (SEM) (Krings et al 2022b) and the elemental composition by EDX (Krings et al 2022a) of the mature radular teeth. The teeth are composed of layers with distinct fibre densities and orientations and show regional differences in the mineral content: the outer, very thin layer of the tooth leading edge (the edge that interacts with the ingesta) contains higher proportions of Ca (~ 7%) (Krings et al 2022b).…”

Mineralize It or Not: Comparative Proteomics and Elemental Analysis Reveal Ancestral Compositions of Iron Mineralized Molluscan Radulae

“…Chitons (from polyplacophoran), 7 limpets (from gastropod), 8 snails (from gastropod), 8 and Aplacophora 9 radulae are equipped with mineralized teeth, while Cephalopoda (including octopus, squid, cuttlefish, nautilus) may have nonmineralized teeth. 10 Because of mineralization at multiple length scales, chiton teeth 11,12 and limpet teeth 13 are reported to exhibit remarkable mechanical properties such as extreme hardness, toughness, and abrasion resistance among all biological materials. Chiton teeth are made of magnetite and apatite, 11 while limpet teeth are made of goethite and silica biominerals.…”

“…13 Other snails have complex compositions and most of them may be calciumbased biominerals. 10 The ultrastructure and composition of chiton teeth have been extensively studied and inspire the synthesis of nanomaterials. 14 Despite numerous studies from a materials perspective, the molecular data underlying their formation is scarce.…”

“…Chiton teeth are made of magnetite and apatite, while limpet teeth are made of goethite and silica biominerals . Other snails have complex compositions and most of them may be calcium-based biominerals . The ultrastructure and composition of chiton teeth have been extensively studied and inspire the synthesis of nanomaterials .…”