A high resolution analysis of the structure and chemical composition of the calcareous corpuscles from Mesocestoides corti.

Mesocestoides corti (syn. vogae), similar to many other cestode platyhelminthes, contains abundant calcium carbonate structures called calcareous corpuscles. These concretions that may constitute as much as 40% of the dry weight of the body, and were proposed to form intracellularly in certain parenchymal cells. As an approach to elucidate the biological role of calcareous corpuscles in cestodes, our aim was to characterize more precisely the structure and topological composition of the corpuscles from M. corti. Employing a variety of high resolution technical approaches, we found that the calcareous corpuscles are spheroid or ovoid layered concretions. They are formed by topographically homogeneous but compositionally heterogeneous layers, suggesting a cyclic process of biomineralization. The layers are composite structures, with granules of tens of nanometers, each surrounded by a cortex of about eight nanometers.

Shell layers of the black-lip pearl oyster Pinctada margaritifera: matching microstructure and composition.

The nacre-prism transition of the mollusc shell Pinctada margaritifera was studied using scanning electron microscopy, electron probe micro-analysis (EPMA) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). Mineralogical change is correlated with a change in organic matrix. Previous analyses had shown that sugars were involved in the transition layer (fibrous aragonite). The new Energy Dispersive Spectrometry (EDS) and TOF-SIMS maps show that the modifications at the layer boundary are complex, and that proteins and lipids are also involved. Detailed TOF-SIMS maps show that the thick organic envelopes surrounding the prisms, and between the prisms and the fibrous aragonitic layer, are not composed by regular layers, but are a patchwork of various molecules. The amino acid compositions of the nacreous and prismatic layer are compared thanks to the TOF-SIMS localized analyses.

Structural, mineralogical, and biochemical diversity in the lower part of the pearl layer of cultivated seawater pearls from Polynesia.

A series of Polynesian pearls has been investigated with particular attention to the structural and compositional patterns of the early developmental stages of the pearl layer. These initial steps in pearl formation bear witness of the metabolic changes that have occurred during the pearl-sac formation. The resulting structurally and biochemically complex structures have been investigated using a variety of techniques that provide us with information concerning both mineral phases and the organic components. Results are discussed with respect to our understanding of the biomineralization mechanisms, as well as for the grafting process.

Soluble organic matrices of aragonitic skeletons of Merulinidae (Cnidaria, Anthozoa).

Our interpretation of the overall taxonomy and evolution of the Scleractinia, the most important reef builders in tropical areas, has long depended exclusively on morphology of the calcareous skeletons. The reported series of physical and biochemical characterizations of skeletons and the mineralizing matrices extracted from the skeletons allow, for the first time, the level of biochemical diversity among corallites of the same family to be estimated. Similarities and differences observed in the micro- and nanostructures of the skeletons reflect those of the soluble organic matrices. Sulphur is mainly associated with sulphated acidic sugars. The role of sulphated sugars on the biomineralization processes is still underestimated. The resulting data suggest that environmental conditions may act on the mineralization process through the detailed compositions of the mineralizing matrices.

Structure and composition of the nacre-prisms transition in the shell of Pinctada margaritifera (Mollusca, Bivalvia).

A microstructural, mineralogical, and chemical study of the nacre-prisms boundary in the shells of Pinctada margaritifera shows that this boundary is not an abrupt transition, but that there exists a distinct fibrous layer with clear topographic structures and evidence of growth lines. A three-step biomineralization process is proposed that involves changes in the chemical and biochemical composition of the last growth increments of the calcite prisms, formation of the fibrous layer, and development of regular tablets in the nacreous layer.

Microstructure and chemical composition of giant avian eggshells.

The microstructure and composition of the layers of two giant avian eggshells were investigated using a combination of scanning electron microscopy, electron probe microanalyses, and X-ray absorption near-edge structure spectroscopy (XANES). The two species have some similarities and differences in their microstructure and composition; the composition is not homogeneous throughout the eggshell thickness. XANES studies show that sulfur is associated with amino acids in the inner organic membranes, whereas in the mineralised layers the sulfur is mainly associated with sulfated polysaccharides. These results are similar to those obtained on chicken eggshells, and confirm the active role of sulfated acidic polysaccharides in biomineralisation processes of carbonate skeletons.