Flabellum chunii Marenzeller 1904
Creators: name: Stolarski, Jarosław
Publisher: name: Zenodo
Year: 2003
Subjects: Biodiversity
Taxonomy
Animalia
Cnidaria
Anthozoa
Scleractinia
Flabellidae
Flabellum
Flabellum chunii

description: Flabellum chunii Marenzeller, 1904   
 Septal morphology.— F. chunii (and some other representatives of traditional Flabellidae) have a scale−like texture on the septal flanks (Fig. 5A 1, A 2). Scale−like units here are composed of bundles of fibers arranged quasi−parallel to septal faces (in Stephanocyathus bundles of fibers are arranged quasi−perpendicularly to the septal faces resulting in their smooth surface). Scale−like structures are developed also on the inner side of the wall, and on the axial junction of the septa. Scale−like units continue on distal, growing edges of skeletal elements where they form small tubercles.   
 Transverse sections.—SEM micrograph of polished and etched sections made approximately in half of the length of S1 (Fig. 5D 1, D 2), shows two zones of different etching relief: (1) dRAF zone (mid−septal zone) composed of series of Ą neighboring pits (dCRA), and (2) TD zone composed of layers of fibers orientated quasi−parallel to the septal surface.   
 The dCRA show twofold structure: inner, deeper hollow is surrounded with circle of short fibers (Fig. 5D 2). The dRAF zone continue between septa and wall (marginotheca, see Stolarski 1995).   
 Longitudinal−radial sections.—Longitudinal sections in the RAF plane show narrow “strands” (ca. 15 µm in width) that are arranged fanwise in the plane of the section (Fig. 6D). Due to the undulating course of RAF in radial and longitudinal directions, dRAF are visible only in some surfaces of the thin−section. In TLM, each “strand” is composed of regular alternations (Fig. 6E) of thicker, brownish, and slightly opaque layers (ca. 1–3 µm width) that are intercalated with thin, rather colorless and more transparent ones (ca. 0.8–1 µm width). Layers within each “strand” have domed shapes, and fade approaching the border of the “strand”. Layers that are brownish in TLM exhibit strong, bright green fluorescence in MFM; thin and transparent layers do not show a chromatic reaction (Fig. 6F). Polished and etched sections viewed in SEM (Fig. 5C 1, C 2) show ca. 15 µm wide “strands” of generally negative etching relief that are composed of regular alternations of domed hollows (ca. 2–3 µm width), separated by small and narrow ridges (ca. 1.5–2 µm width).   
Elemental (C, S, Sr, Mg) X−ray mapping of polished sections using wavelength−dispersive techniques (WDS) showed an overall homogenous distribution of S, Sr and Mg (the latter is a trace element). However, “strands” as viewed in TLM (Fig. 6A), or darker regions as viewed in BSE mode (Fig. 6B), are enriched in carbon (Fig. 6C).  
 Sectionperpendiculartothewall.—Polished and etched sections perpendicular to the marginothecal wall (Fig. 5B) show overall continuity of layers of fibers between dRAF and TD. The main difference between these regions is negative etching relief of broader zones in dRAF region and only narrow zones of negative relief between fiber layers in TD; pattern of layers continuing between dRAF and TD zones is very similar to that observed in S.paliferus in section perpendicular to the septum, however, in Flabellum TD are formed primarily on the inner wall side (layers that continue on outer side of the wall, named tectura by Stolarski (1995), are narrow and fade downwards).
description: Published as part of Stolarski, Jarosław, 2003, Three-dimensional micro- and nanostructural characteristics of the scleractinian coral skeleton: A biocalcification proxy, pp. 497-530 in Acta Palaeontologica Polonica 48 (4) on pages 503-505, DOI: 10.5281/zenodo.13388790