Stylophyllum paradoxum Frech, 1890

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 : 512-517

Stylophyllum paradoxum Frech, 1890

Traditionally, stylophyllinans are considered as non−trabecular corals ( Cuif 1973; Beauvais 1982; Roniewicz 1989) i.e., with skeleton built entirely of fibrous sclerenchyme not organized into “continuously growing rods formed by fibers [...], provided with an axis” (clue of trabecula definition in Roniewicz and Stolarski 1999: 165). Contrary to this generalized diagnosis, Stolarski and Russo (2002) suggested that stylophyllids (a major group of stylophyllinans) have skeletons much more microstructurally diversified. There are at least four main microstructural patterns recognized in septal transverse sections; in two of them distinct “centers of calcification” occur ( Stolarski and Russo 2002: 662, fig. 11). Stolarski and Russo (2002) noted that stylophyllid “centers of calcifications” (when present) differ from typical “centers of calcification” of e.g., “thick−trabecular” corals in the lack of a distinct 10–20 µm wide “border layer ” (“border layer” is illustrated herein in Platygyra daedalea , and Galaxea fascicularis — Figs. 10A , 11E ). This results in a clear separation of “centers of calcification” from adjacent fibrous parts of the skeleton in non−stylophyllid corals and a lack of this separation in stylophyllids. Herein, more details are given about the skeleton of Stylophyllum paradoxum Frech,1890 included into the 3 rd microstructural group by Stolarski and Russo (2002). Stylophyllids belonging to this category have single and large “centers of calicification” revealed in transverse sections of septal spines.

Transverse sections.—In polished transverse section, in TLM the middle portion of corallum shows a multilayered structure in septal spines. Borders between particular fibrous layers are darker than fibers comprising concentric layers. More central parts of the septal spine (ca. 0.5 mm in diameter) are often differentiated from the outer part of the spine by darker or occasionally lighter appearance ( Fig. 13A, B ).

Longitudinalsectionofseptalspine.—TLM shows that there are several superimposed fibrous layers that comprise the septal spine. In the central part of the spine, crescent zones infilled by spar (ca. 30 µm in width) alternate regularly with typical fibrous layers (ca. 30–40 µm in width)— Fig. 13C–F . Each septal spine includes only one zone with fibrous/spar alternations. Fibrous layers from the central septal spine continue into layers that are thickening the septum (e.g., Fig. 13E, F ).

Pachythecaliina: Pachysolenia cylindrica Cuif, 1975 , Pachythecalis major Cuif, 1975 , and Zardinophyllum zardini Montanaro−Galitelli, 1975

Many pachythecaliinan skeletal features are unique among skeletonized anthozoans from the earliest Mesozoic, i.e.: (1) a very thick wall (pachytheca), the predominant skeletal character has aragonite fibers arranged in penicillate units, which increase centripetally, (2) non−exsert septa, usually located deeply in the calice, and (3) strong bilateral symmetry in initial and juvenile stages (adult coralla may have quasi−radial symmetry), all discussed by Cuif 1975; Stolarski 1999; Roniewicz and Stolarski 2001; Stolarski and Russo 2001. Their skeletal features are, in comparison with other fossil corals, well characterized, although some important microstructural skeletal characters have not been sufficiently well characterized. For example, there are doubts about the microstructure of the narrow pachythecaliinan dRAF zone: traditionally septa of all genera are considered non−trabeculate ( Cuif 1975), on the other hand Iljina (1984) suggested that in Pachysolenia ( P. primorica Iljina, 1984 ) they are composed of “trabeculae in series”. The suggestion that separated “centers of calcification” may actually occur in septa of Pachysolenia and Pachythecalis was recently re−examined by Stolarski and Russo (2001: 245). Another unknown microstructural aspect of the pachythecaliinan skeleton is growth zonation of fibers in pachytheca. Cuif, Dauphin, and Gautret (1999: 591) suggested that in Pachythecalis major , the “internal organization of fibers does not show visible traces of the usual cyclic secretory process”, and later they added that, “obviously, additional aragonitic component has been added during the fossilization process, possibly as syntaxial deposit” ( Cuif, Dauphin, and Gautret 1999: 591). However, evidences of regular diagenetic alterations within fossil pachythecaliinan skeleton have not been provided. The purpose of this work was to supplement observations by previous authors about the original structure of dRAF and pachythecal TD deposits.

Pachysolenia cylindrica Cuif, 1975 .—TLM of a transverse section of pachytheca shows bundles of fibers with regular, faint 5–8 µm alternations of lighter and darker zones perpendicular to growth ( Fig. 14A, F ). In SEM, a polished and etched section of pachytheca (same as viewed in TLM) may occasionally show regions with negative and positive etched relief distributed with a periodicity similar to that seen in TLM for lighter and dark zones. However, in contrast to zones with etched TD fibers regularly tapered e.g., in fossil unidentified conophyllid ( Fig. 12C ), in P. cylindrica negatively etched regions have a “carved” appearance and continue between larger bundles of fibers ( Fig. 14H ). Sr and Mg WDS mapping of pachytheca show non−homogenous distribution of these elements (in non−altered aragonite skeletons of extant Scleractinia Sr (and traces of Mg if any) are homogenously distributed at comparable magification). In Pachysolenia, Sr shows enrichment in regions (arrows in Fig. 14B, C ) where Mg appears depleted.

The septal dRAF zone in transverse section viewed in TLM and SEM ( Fig. 14G ) seems to be homogenous and not differentiated into separate dCRA. The dRAF zone in TLM of longitudinally sectioned septa (which are very thin and undulating) consists of darker bundles of quasi−parallel fibers occasionally separated by “amorphous” and lighter layers ( Fig. 14D, E ). Fibers are perpendicular to the distal septal margin and not separated by distinct borders as in dRAF zones of extant corals illustrated herein (compare e.g., Figs. 2E, 5C, 6D, 7F).

Pachythecalis major Cuif, 1975 .—The thick theca of this species, which occurs with Pachysolenia cylindrica in the same locality, in transverse, polished section shows faint regular (ca. 7 µm) alternations of lighter and darker zones within bundles of fibers ( Fig. 15A 3). Transverse septal and longitudinal sections through the dRAF zone show the same microstructural organization as in P. cylindrica , however, occasionally the homogenous dRAF zone is interrupted and forms elongated and individualized regions ( Fig. 15A 1 , A 2).

Zardinophyllumzardini Montanaro−Galitelli, 1975.—This is the only pachythecaliinan species that occurs in the same locality (Alpe di Specie) as the unidentified conophyllid that preserves extremely faint microstructural details of the skeleton. Similar to other pachythecaliinans, Z. zardini has smooth septal edges ( Fig. 15B 1 ). In contrast to specimens from Alakir Çay, Turkey ( Pachysolenia , Pachythecalis ), a majority of Z.zardini specimens have components of the former dRAF zone removed or possibly dissolved, and this region is easily recognized as a narrow fissure ( Fig. 15B 2). In the few specimens with a solid dRAF zone, it appears to be composed of transparent homogenous material (not differentiated into separate centers) that most likely is secondary infilling. On the other hand, the rest of the skeleton seems very well preserved. Polished and etched bundles of pachytheca fibers of Z. zardini , transverse sections exhibit more or less regular etching banding every ca. 7–10 µm that appears alike the etching pattern of TD fibers in extant corals ( Fig. 15B 2). The “lamellar layer” noted for the first time by Cuif (1975) can also be discerned as a densely layered zone (in contrast to non−layered sparry calcite in the calicular center) “coating” intracalicular structures, i.e., wall ( Fig. 15B 2).

Figures

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.

Fig. 11. Platygyra daedalea (Ellis and Solander, 1786); ZPALH.23/8 (originally NMNH A.G. Humes collection. Acc. number 274378). Recent, 25 m, north of Ankazo−beravina, near Nosy Be, Madagaskar, August 24, 1967. A. Transverse polished section of septum in TLM; note brownish “calcification centers” (dRAF), regular growth increments of fibers (e.g., in encircled area), and dark brown regions (red arrows) of filaments of endolithic organisms (most likely algae, fungi). B. The same septal fragment as A, stained with acridine orange in MFM view; dRAF exhibit very light, green−yellow fluorescence; higher magnifications (C) show delicate greenish bands matching organic components trapped between successive growth increments of fibers (white arrows). D. Transverse polished section of septum in TLM; dRAF in lower right corner; regular growth increments of fibers (TD) are emphasized by levels of brownish bands. E. SEM micrograph of transverse polished and etched section of septum; fibers adjacent to row of dRAF (“calcification centers”) taper regularly at ca. 3 µm matching brownish bands in D.

Fig. 13.Stylophyllumparadoxum Frech, 1890, NHMW 1982/57/100, corallum with aragonitic mineralogy still preserved. Triassic, Rhaetian, Fischerwiese, Northern Calcareous Alps, Austria. A, B. Transverse section of septa with concentric arrangement of fibers within septal spines (B, enlargement). C–F. Longitudinal sections crossing centers of septal spines; domed, successive layers of aragonite fibers (darker) separated by lighter “voids” infilled by spar (see D, F enlargements). Except for regular voids in spine centers, there is no difference in organization of superimposed layers of fibers within septal spine. All TLM micrographs.

Fig. 14. Pachysolenia cylindrica Cuif, 1975, ZPALH. XXI/4. Triassic, Lower Norian. Alakir Çay,Turkey. A–C. Complementary regions of transversely sectioned and polished pachytheca: TLM image (A), greyscale Sr (B) and Mg (C) mapping acquired on the electron microprobe by wavelength−dispersive techniques; darker areas equal very low concentration whereas lighter areas equal slightly higher concentrations. Sr (in B) shows enrichment, at least in some regions (arrows) where Mg (in C) appears depleted. Sr mapping of diagenetically non−altered fibrous parts of coralla of extant corals (not illustrated here) invariably shows nearly homogenous distribution of this element. D. TLM view of longitudinally sectioned pachytheca and septum; part of the preserved septum encircled and enlarged in E to show “non−trabecular” nature of dRAF. F. Transverse polished section of pachytheca in TLM; fibers show faint regular 5–8 µm alternations of lighter and darker zones. G. Homogenous septal dRAF zone in SEM view of transversely polished and etched section. H. Transverse polished and etched section of pachytheca (SEM); fibrous skeleton shows negative and positive etching relief (at ca. 5–8 µm distance).

Fig. 12. Undetermined conophylliid. ZPALH.23/9. Triassic (Middle Carnian), San Cassiano Beds, Alpe di Specie, Dolomiti (Italy), corallum still wi th aragonitic mineralogy preserved. B. Transverse polished section of corallite in TLM (A); enlarged portions of longitudinally sectioned septa with regular growth increments of fibers (B). C. Longitudinally polished and etched section of septum with fibers regularly tapered (SEM). D. Transverse, polished and etched septum (SEM) with dCRA (“center of calcification”, arrows). E. Septum longitudinally sectioned in dCRA region with domed, successive layers of fibers and occasional (arrow) larger voids between them.

Fig. 15. A. Pachythecalis major Cuif, 1975, ZPAL H.23/10. Triassic, Lower Norian. Alakir Çay,Turkey. Transverse polished corallite in TLM (A1); enlargement of dRAF (A2). A3. Transverse polished pachytheca in TLM; fibers show faint regular (ca. 7 µm) alternations of lighter and darker zones. B. Zardinophyllum zardini Montanaro−Gallitelli, 1975. Triassic (Middle Carnian), San Cassiano Beds, Alpe di Specie, Dolomiti (Italy). Completely smooth RAF of septum in distal view, IPUM11 (B1, SEM). B2. Transverse, polished and etched septum (ZPALH.23/11); note fissure in dRAF region (arrow), more or less regular discontinuities in arrangement of pachytheca fibers (arrows), and secondary, probably biogenic deposits filling up the calice (marked transparent dark grey). All coralla with still preserved aragonitic mineralogy.

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).