Dillaman R M, Hart H V
Scan Electron Microsc. 1981(Pt 3):313-20.
Coronal plates of the sea urchin Strongylocentrotus purpuratus have a microstructure typified by smooth textured trabeculae. When plates were decorated with calcite crystals each rhombohedron had the same orientation regardless of its location on the plate. When the sample was oriented so that the three edges of the rhombohedron formed equal 120 degrees angles and the three crystal faces appeared to form equal angles with the plane of the photograph, the c-axis of the plate paralleled the electron beam and the three a-axes were 30 degrees counterclockwise from the edges. These a-axes were then related to a plate edge recorded in a low magnification micrograph. Directions of the a-axes of each plate were also measured using a back-reflection Laue x-ray diffraction camera. A comparison of a-axes measured by the two techniques showed an average difference of 3 degrees, indicating that decorated crystal grew in crystallographic continuity with the plate. Assuming this relationship remains constant, the decoration technique appears to be an accurate and efficient method for evaluating the crystallography of echinoid skeletal units. Analysis of a polar plot of a-axes for 11 plates indicated that the a-axes were not randomly oriented; however, definitive relationships must await more extensive investigations.
紫球海胆的冠状板具有以纹理光滑的小梁为特征的微观结构。当用方解石晶体装饰这些板时，每个菱面体无论在板上的位置如何都具有相同的取向。当样品取向使得菱面体的三条边形成相等的120度角，并且三个晶面与照片平面似乎形成相等的角度时，板的c轴与电子束平行，并且三个a轴从边缘逆时针方向成30度。然后将这些a轴与低倍显微镜照片中记录的板边缘相关联。还使用背反射劳厄X射线衍射相机测量每个板的a轴方向。两种技术测量的a轴比较显示平均差异为3度，表明装饰晶体与板在晶体学上连续生长。假设这种关系保持不变，装饰技术似乎是评估海胆类骨骼单元晶体学的一种准确而有效的方法。对11个板的a轴极坐标图的分析表明，a轴不是随机取向的；然而，明确的关系还需更多广泛的研究。
