Three-dimensional micro- and nanostructural characteristics of the scleractinian coral skeleton: A biocalcification proxy Author Stolarski, Jarosław text Acta Palaeontologica Polonica 2003 2003-11-30 48 4 497 530 journal article 1732-2421 “ Ceratotrochus” magnaghii Cecchini, 1914 Morphology .—Overall, septa of “ C. ” magnaghii have smooth distal margins as in S. paliferus and D. dianthus . However, in contrast to the previous two species, they remain nearly completely smooth, even in much higher magnification ( Fig. 8A 1 , A 2 ). SEM enlargement of distal septal margins shows their smooth surface, which is not differentiated into “patches” or tubercles. Similarly to e.g., S. paliferus , the structure of the septal margin regular “grains” ca. 500nm in diameter can be distinguished ( Fig. 8A 3 ). The generally straight course of the ca. 15 µm wide distal septal margin may show a gently zigzaging deviation towards granules on the septal flanks. Except for granulations, the septal surface is smooth. Transverse sections .—Two zones of different etching relief can be distinguished in SEM view of sections made approximately in half of S1 ( Fig. 8B ): (1) a homogenous dRAF zone ca. 15 µm wide that has negative etching relief, and (2) TD zone of overall positive relief, except for the borders between bundles of fibers that are distributed more or less regularly every 7–10 µm. Longitudinal−radial sections .—In contrast to a seemingly homogenous structure of dRAF zone as seen in SEM, longitudinal sections in the RAF plane reveal very narrow strands, ca. 5 µm wide and approximately parallel to each other but arranged fanwise in the plane of the entire section ( Fig. 8C 1 , red arrows). These longitudinal “strands” have a layered structure, which is particularly well visible on the entire surface of the section ( Fig. 8C 1 , C 2 ). Wider, dark−brown layers are 3.7–4.6 µm thick, whereas thin, transparent and much lighter layers are ca. 1.8 µm wide. Only dark−brown skeletal components stained with acridine−range dye exhibit bright green−yellow fluorescence ( Fig. 8C 3 ).