Stephanocyathus paliferus Cairns, 1977

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 : 499-500

Stephanocyathus paliferus Cairns, 1977

Septalmorphology.—Septa have a smooth, non−denticulated distal margin typical of traditional caryophylliinans ( Fig. 1A–C ) 1. SEM close−ups of the septal margin show slightly irregular, rounded “patches” (ca. 5–20 µm in diameter) whose surface has a grainy texture, which results in the exposure of angular or somewhat rounded “microcrystalline” components, 300–500 nm in diameter ( Fig. 1E ). These “patches” cover the entire length of the distal septal margin, which is rounded and only 50–100 µm wide. In places, the straight course of the distal margin has a zigzag deviation to sites with granular or longitudinal ridge−like structures (“ornamentation”) appearing on septal flanks ( Fig. 1D ). The septal surface between granulae is smooth.

Transversesections.—Two zones of different light−transparency properties and colors are distinguishable in transverse sections made approximately throughout half the length of S1 and viewed in TLM (Fig. 2C): (1) a dRAF zone (mid−septal zone), with darker, slightly opaque brownish coloration (“dark line”), and (2) a TD zone of transparent, nearly colorless fibers, that borders the dRAF zone. The dRAF zone has a slightly wavy course and is ca. 50 µm in width; it is not homogenous but is composed of rounded spots (ca. 20 µm in diameter) with a higher concentration of dark brown components that are fairly regularly distributed. The skeleton adjacent to the dRAF zone is composed of bundles of fibers (TD), quasi−perpendicularly orientated to the dRAF plane. In MFM, skeleton stained with acridine orange dye exhibits a twofold chromatic response (Fig. 2D). Patches exhibiting bright green fluorescence perfectly match those in TLM having brown coloration within the dRAF zone. Chromatic response of TD is much less prominent, and green−orange fluorescence is localized at borders between fibrous layers and also at borders between individual bundles of fibers. In polished, etched sections (SEM), dRAF exhibits a negative relief, whereas TD generally shows positive etching relief, except for the borders between layers of fibers (especially borders parallel to septal faces; Fig. 3A). On the bottom of dRAF etched hollows some crystalline structures can be discerned ( Fig. 3B).

Longitudinal−radialsections.—Fig. 2A shows an S 1 in TLM cut precisely in the mid−septal plane. Due to the slightly undulating course of RAF, dRAF are not visible on the entire surface of this thin−section. In fact, only some brownish spots that mark the position of sectioned dRAF (Fig. 2A, B) are those that are truly exposed; some others are located slightly beneath the surface of the section and visible only using transmitted light (and not SEM, for example). In spots where dRAF are easily visible (Fig. 2B–E) they form “strands” ca. 20–30 µm in width more or less parallel to each other; however, they are arranged fanwise in the plane of the entire section (Fig. 2A). Each “strand” is composed of regular alternations of thicker, brownish, and slightly opaque layers (ca. 5–6 µm width) that are intercalated with thin, rather colorless and more transparent ones (ca. 1.5–2 µm width). Layers within each “strand” have domed shapes, and fade approaching the border of the “strand” (Fig. 2E, yellow arrow), or may continue between “strands” (Fig. 2E, pink arrow). Only those layers that are brownish in TLM exhibit strong, bright green fluorescence in MFM, whereas thin and transparent layers do not show a chromatic reaction (Fig. 2F). Some corresponding “strands” (compare Fig. 2E and Fig. 2F) do not exhibit in MFM strong chromatic reaction, most likely because some “strands” are actually located inside the thin−section as mentioned above, hence, were not exposed to the

1 Stolarski (2000) showed that the seemingly smooth distal edge of the septa in some caryophylliinans (i.e., traditional guyniids), as seen at lower magnification, may actually consist of tiny denticulations ( Stenocyathus , Truncatoguynia ) or indeed, be nearly completely smooth at higher magnification ( Guynia ). In this respect, the distal septal margin of S. paliferus is intermediate between that of Guynia and Stenocyathus , and resembles especially that of Lophelia pertusa (Linnaeus, 1758) , described as “built of densely packed accumulation of centers of calcification” ( Cuif and Dauphin 1998: 263, fig. 3.7).

acridine orange dye. Scanning electron micrographs of polished and etched sections correspond to those viewed in TLM: ca. 20–30 µm wide “strands” of generally negative etching relief are composed of regular alternations of domed hollows (ca. 5–6 µm width), separated by small and narrow ridges (ca. 1.5–2 µm width), Fig. 3C, D. Layers within each “strand” fade approaching the border of the “strand” or continue between neighboring “strands” ( Fig. 3C). The narrow ridges are composed of fibers perpendicular to their course; similar but longer fibers are seen in the bottom of wider etching hollows. At higher magnifications, fibers that form ridges or are visible on the bottom of hollows exhibit a lumpy texture. Polished (but not etched) sections prepared for use in AFM, show very small and shallow grooves, difficult to discern under low magnification of a dissection scope. AFM images of these hollows reveal aggregations of grains that are ca. 50 nm in diameter ( Fig. 4A–E ). Their size most likely matches that of lumps on fibers viewed in SEM; however, because of better resolution the size of these particles is based on AFM observations. The skeleton bordering shallow grooves also shows, in some places, nanogranular texture, however, only in grooves individual grains are well exposed.

Section perpendicular to the septal plane.—In this section, only one, relatively narrow region of dRAF occurs. Fig. 3E, F shows a polished, lightly etched section with the dRAF region having negative relief, which is bordered with TD that have positive etching relief, except for the borders between layers of fibers. There is an overall continuity of layers of fibers between dRAF and TD; most fiber layers visible in the center of dRAF are still traceable within the TD. Only in same places individual layers visible in dRAF may disappear towards the TD. The basic difference between these two regions is a distinct negative etching relief of broader zones in dRAF, and only very narrow zones of negative relief at borders between fiber layers in TD.

Fig. 2. Stephanocyathuspaliferus Cairns, 1977. ZPALH.23/1. Locality data as in Fig. 1. A, B . TLM micrographs of longitudinal polished sections in RAF Ą plane. C, D. Transverse polished section of septum in TLM (C) and MFM (D). Organic components of dRAF (brownish in C) stained with acridine orange show bright−green fluorescence (D). Chromatic response of TD is much less prominent. E, F. TL M (E) and MFM (F) micrographs of enlarged part of longitudinally sectioned septum shown in B. Organic and mineral phases of dRAF regularly alternate; only organic components exposed and stained with acridine orange fluoresce with bright−green light.

Figures

Fig. 1. Stephanocyathuspaliferus Cairns, 1977. ZPALH.23/1 (originally NMNH 46443 lot). Recent, south of Bonaire, 11°18.8’N, 68°22’W, 384–607 m. Pills sta. P−753. July 26, 1968. A–C. Distal (A), lateral (B), and proximal (C) views of corallum. D, E. SEM of septa and paliform lobes. D. Arrow indicates portion of septum enlarged on E. E. “Patches of microcrystals” (fasciculi of Wise 1972) at the growing septal edge here called the Rapid Acretion Front (RAF).

Fig. 4. Stephanocyathuspaliferus Cairns 1977. ZPALH.23/1. Locality data as in Fig. 1. A–C. AFM (contact mode): height—2D projection (A), phase (B), and height—3D projection (C) images of 5 m2 polished (not etched) septum sectioned in RAF plane; AFM tip was placed in dRAF “strand” region as seen in etched sections (Fig. 3C). D, E. AFM (tapping mode) height—2D projection (D) and phase (E) images of spherical bodies seen on the bottom of dRAF “strand”.