title: Initial formation of calcite crystals in the thin prismatic layer with the periostracum of Pinctada fucata.
abstract: Although the formation mechanism of calcite crystals in the prismatic layer has been studied well in many previous works, the initial state of calcite formation has not been observed in detail using electron microscopes. In this study, we report that the soft prismatic layer with transparent color (the thin prismatic layer) in the tip of the fresh shell of Pinctada fucata was picked up to observe the early calcification phase. A scanning electron microscope (SEM) image showed that the growth tip of the thin prismatic layer was covered by the periostracum, which was also where the initial formation of calcite crystals began. A cross-section containing the thin calcite crystals in the thin prismatic layer with the periostracum was made using a focused ion beam (FIB) system. In a transmission electron microscope (TEM) observation, the thin calcite crystal (thickness is about 1μm) on the periostracum was found to be a single crystal with the c-axis oriented perpendicular to the shell surface. On the other hand, many aggregated small particles consisting of bassanite crystals were observed in the periostracum suggesting the possibility that not only organic sulfate but also inorganic sulfates exist in the prismatic layer. These discoveries in the early calcification phase of the thin prismatic layer may help to clarify the mechanism of regulating the nucleation and orientation of the calcite crystal in the shell.
authors.affiliation: Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. amichiwo@mail.ecc.u-tokyo.ac.jp
authors.forename: Michio
authors.initials: M
authors.lastname: Suzuki
authors.forename: Seiji
authors.initials: S
authors.lastname: Nakayama
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Nagasawa
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Kogure
mesh_terms: D060105:Animal Shells / Q000254:growth & development / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D000818:Animals; D002113:Calcification, Physiologic; D002119:Calcium Carbonate / Q000378:metabolism*; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D049911:Pinctada / Q000254:growth & development / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D002119:Calcium Carbonate