Abstract
Molluscan shells, which are typical examples of such biominerals, are composed of mainly inorganic calcium carbonate crystals and less amounts of organic matter. The organic matter forms matrices, such as sheaths, envelopes, walls and sheets, to regulate the polymorph, orientation, shape, and texture of the crystals. Besides, calcium carbonate crystals in shells contain a certain amount of intracrystalline organic macromolecules such as proteins and polysaccharides. The size of the molecules is several nanometers which can be visualized as Fresnel or Z contrasts by TEM/STEM imaging. From the distribution of the molecules in the crystals, it is inferred that the multi-layer structure of the larval shell and mosaic structure of the columnar layer in bivalve shells are constructed by non-uniform incorporation of such macromolecules.
