Université de Lille I, CNRS, Laboratoire Géosystèmes, 59655 Villeneuve d'Ascq, France.
Microsc Microanal. 2013 Dec;19(6):1511-22. doi: 10.1017/S1431927613013226. Epub 2013 Sep 10.
Testate amebae are unicellular shelled protozoa commonly used as indicators in ecological and paleoecological studies. We explored the potential application of three-dimensional (3D) X-ray micro-tomography used in addition to 2D techniques (environmental scanning electron microscopy, electron probe micro-analysis, and cathodoluminescence) for detailed characterization of agglutinated shells of protozoa. We analyzed four specimens of the aquatic testate ameba Difflugia oblonga (Arcellinida), to test whether size distribution and mineral composition of shell grains diverged from sediment size distribution and mineralogical composition. From the 3D images, the geometry of the specimens (size and mass) and of the individual grains forming the specimen (grain size distribution and volume) were calculated. Based on combined chemical, mineralogical, and morphological analyses we show that D. oblonga is able to selectively pick up the small size fraction of the sediment with a preference for low-density silicates close to quartz density (~2.65). The maximum size of the grains matches the size of the pseudostome (shell aperture), suggesting the existence of a physical limit to grain size used for building the shell. This study illustrates the potential of this combined approach to characterize agglutinated shells of protozoa. This data can be useful for detailed morphological studies with applications in taxonomy and ecology.
有壳原生动物是单细胞原生动物，通常用作生态和古生态学研究的指标。我们探讨了三维（3D）X 射线微断层扫描技术除二维技术（环境扫描电子显微镜、电子探针微分析和阴极发光）之外，在详细描述原生动物胶结壳方面的潜在应用。我们分析了四个水生有壳原生动物片形目（Arcellinida）的变形虫（Difflugia oblonga）标本，以测试壳粒的大小分布和矿物组成是否与沉积物的大小分布和矿物组成不同。从 3D 图像中，我们计算了标本的几何形状（大小和质量）以及形成标本的单个颗粒的几何形状（颗粒大小分布和体积）。基于综合的化学、矿物学和形态学分析，我们表明变形虫能够选择性地摄取沉积物中的小粒径部分，优先选择接近石英密度（~2.65）的低密度硅酸盐。颗粒的最大尺寸与假口（壳孔）的尺寸相匹配，这表明用于构建壳的颗粒尺寸存在物理限制。这项研究说明了这种组合方法在描述原生动物胶结壳方面的潜力。这些数据可用于具有分类学和生态学应用的详细形态学研究。
