Study on the microstructure of biocrystals in invertebrates and its phylogeny

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In this study, the microstructure of biomineral and the shell structure were examined by the use of electron and optic microscopes. For elucidating the mechanism of shell formation, the biocrystal growth on the inner shell surface of about twenty species of gastropods was observed. There are two types in nacreous growth, namely pillar and sheet nacreous growth. The crossed lamellar growth of gastropods is similar to one of pelecypods. Aragonite and calcite crystals grow at the same area.Especially, the shell structure of Monodonta and so on was examined in details. As the result, many features of gastropodian shells are common to ones of pelecypods. But, there are some different points in the development of the most inner shell layer, the formation of trans-prismatic layer and the nature of crossed lamellar and nacreous structures.The ultra-microstructure of biocrystals was examined by transmitted electron microscope. It was observed that the third order lamellae of aragonite crystal in the shell of Barbatia are not a single crystal, but polysynthetically twinned crystals. The composite plane of the polysynthetic twinning is (110) plane. The thickness of polysynthetic twin individuals is several hundreds - less than a hundres A. Aragonitic biocrystals of homogeneous and nacreous structures form also twin structure.Epithelial calcified tissues of invertebrates had differetiated at the stage of protozoa and higher animals succeeded to them. Calcreous shell and organic layers differentiated in the course of biological evolution. Organic matrixes of the former originated from homologous materials of glico-calyx and crystal deposition in organic matrixes was gained in relation to metabolic activity.