5:15 PM - 7:15 PM
[BPT03-P03] Visualization of microstructure on the shell surface of benthic foraminifera by EBSD method
Keywords:foraminifera, calcium carbonate, crystal orientation, EBSD, biomineralization
Biominerals serve various functions in living organisms. Calcareous foraminifera forms protective shells (i.e. tests) composed of calcium carbonate which are valuable paleoenvironmental proxies. Hence foraminiferal shells have been extensively studied from both environmental and biological perspectives, however, the details of the mineralogical microstructure, including crystal orientation and grain structure of calcium carbonate crystals that constitute the shell, have not been fully understood. Recently, the ultra-micro structure of the shell has been observed by electron microscopy (Nagai et al., 2018), but it is not clear how the size and orientation of the calcium carbonate crystals are distributed extensively across the shell. Electron Backscatter Diffraction (EBSD) method has enabled millimeter scale visualization of crystal structure and crystal orientation. In this study, we performed morphological observations with a field emission scanning electron microscopy (FE-SEM) and crystallographic orientation analysis of shell surfaces of three species of benthic foraminiferal test by using EBSD, to visualize the microstructures that appear on them.
We analyzed three species, Ammonia confertitesta, Hoeglundina elegans, and Spirillina vivipara, which are phylogenetically distant. The results revealed similarities and differences in the crystallographic orientation and crystallographic phases of the calcium carbonate crystals that compose the shells. Although A. confertitesta and H. elegans were formed by different polymorphs, calcite and aragonite, respectively, calcium carbonate crystals in both species showed a crystallographic preferred orientation of the c-axis, which was oriented perpendicular to the shell surface. Domains of the same crystallographic orientation on the foraminiferal surface were similar in shape and size. Calcite crystals of S. vivipara also showed a crystallographic preferred orientation of the c-axis, but unlike the other two species, it was oriented horizontally to the shell surface.
The characteristics observed in each species could reflect their respective habitat, evolutionary processes, and growth patterns.
Reference
Y. Nagai, K. Uematsu, R. Wani, T. Toyofuku (2018), “Reading the Fine Print: Ultra-Microstructures of Foraminiferal Calcification Revealed Using Focused Ion Beam Microscopy”, Frontiers in Marine Science 5, doi: 10.3389/fmars.2018.00067
We analyzed three species, Ammonia confertitesta, Hoeglundina elegans, and Spirillina vivipara, which are phylogenetically distant. The results revealed similarities and differences in the crystallographic orientation and crystallographic phases of the calcium carbonate crystals that compose the shells. Although A. confertitesta and H. elegans were formed by different polymorphs, calcite and aragonite, respectively, calcium carbonate crystals in both species showed a crystallographic preferred orientation of the c-axis, which was oriented perpendicular to the shell surface. Domains of the same crystallographic orientation on the foraminiferal surface were similar in shape and size. Calcite crystals of S. vivipara also showed a crystallographic preferred orientation of the c-axis, but unlike the other two species, it was oriented horizontally to the shell surface.
The characteristics observed in each species could reflect their respective habitat, evolutionary processes, and growth patterns.
Reference
Y. Nagai, K. Uematsu, R. Wani, T. Toyofuku (2018), “Reading the Fine Print: Ultra-Microstructures of Foraminiferal Calcification Revealed Using Focused Ion Beam Microscopy”, Frontiers in Marine Science 5, doi: 10.3389/fmars.2018.00067