Galaxea fascicularis ( Linnaeus, 1767 )

Stolarski, Jarosław, 2003, Three-dimensional micro- and nanostructural characteristics of the scleractinian coral skeleton: A biocalcification proxy, Acta Palaeontologica Polonica 48 (4), pp. 497-530 : 508-510

Galaxea fascicularis ( Linnaeus, 1767)

Morphology.—Septa of G. fascicularis show scale−like texture similar to that in F.chunii ( Fig. 9A, B ), however, the pattern of scale−like units arrangement is less regular (“Persian lamb” style) than in F. chunii (regular, “roof−tile” style). Scale−like units cover all intracalicular surfaces, and continue on distal, growing edges of skeletal elements in a form of neighboring small tubercles ca. 15 µm across ( Fig. 9A ).

Transversesections.—Two zones of different light−transparency properties and colors are recognized in transverse section of S 1 in TLM ( Fig. 10A ): (1) dark−brown, partly opaque dRAF zone, and (2) TD zone composed of transparent fibers. In the central part of the septum, dRAF are bordered with homogenous zone of TD fibers (ca. 10 µm wide). Outwards from this zone, TD fibers show very regular alternations (ca. every 3–5 µm) of thin darker layers, and slightly thicker, lighter layers ( Fig. 10A , red arrows). In the more axial part of this sectioned septum, TD fibers are inclined towards the corallite center ( Fig. 10C ). Bundles of fibers are gently outlined by brownish borders and similar to the more central part of septum, show regular alternations of darker and lighter layers. In SEM view of polished and lightly−etched section of axial part of septum, dRAF (or distinct dCRA) that have negative etching relief are bordered by crescent−shaped zones of fibers. On both sides of the dRAF zone, bundles of fibers are inclined towards the corallite center and are regularly tapered every 3–5 µm ( Fig. 10B , red arrows). In more central part of the septum, dRAF also have negative etching relief (occasionally, with some amorphous material in the center). The only difference with more axial parts of the septum is that bundles of fibers are arranged more perpendicularly to the septal faces ( Fig. 9C, D ). In MFM view, illustrated in Fig. 10C axial part of septum stained with acridine orange show two zones of different chromatic response ( Fig. 10D ): dRAF exhibit bright yellow−green fluorescence, whereas borders between bundles of TD fibers show less prominent, greenish fluorescence. Regular alternations of brownish and more transparent zones viewed within fibers in TLM view ( Fig. 10A , and less prominent in Fig. 10C ) are not been emphasized in MFM.

Longitudinal−radial sections.—Polished and etched sections, made in the septal RAF plane, show regular alternations of regions in SEM, with negative (domed hollows) and positive (ridges) etched relief ( Fig. 9E, F ). Regions with negative and positive relief alternate approximately every 5 µm, but layers ca. 2–3 µm also have been observed ( Fig. 9F ).

Figures

Fig. 9. Galaxea fascicularis (Linnaeus, 1767); ZPAL H.23/7 (originally NMNH 90860 lot). Recent, North Pacific Ocean, Central Philippines (southern parts of islands), collection J.B. Steere. A, B. Morphology of distal septal edge (A) and septal flank spine (B). Note “Persian lamb” texture of skeletal surface (as shown by these fasciculi). C, D. Transverse section of polished and etched septum. Arrow in enlarged (D) fragment (general view in C) shows “blurry”, probably organic material in dCRA and adjacent, radiating TD fibers (ca. 3–5 µm growth increments). E, F. Septum longitudinally sectioned in RAF plane; note dissolved/etched dRAF components in longitudinal “strand” (F enlargement). All are SEM.

Fig. 10. Galaxea fascicularis (Linnaeus, 1767); ZPAL H.23/7 (originally NMNH 90860 lot). Recent, North Pacific Ocean, Central Philippines (southern parts of islands), coll. J.B. Steere. A. Transverse polished section of septum in TLM; note dRAF in lower right corner (brown “calcification center”) and regular growth increments of TD fibers (red arrows). B. SEM of transverse (slightly oblique) polished and etched section of septum; fibers adjacent to dRAF (bottom) show regular tapering periods at ca. 2–3 µm: red arrows). Oblique sectioned dRAD, with dissolved/etched inner components have crescent appearance. C. Transverse polished (slightly oblique) section of septum, TLM view; dRAF show brownish coloration; borders between bundles of fibers only gently outlined (white arrows). D. The same septal fragment as C, stained with acridine orange in MFM view; dRAF exhibit light, green−yellow fluorescence, whereas borders between bundles of fibers (arrows) emphasize greenish fluorescence.