Furcophyllia shaitanica, Melnikova & Roniewicz, 2007

Melnikova, Galina K. & Roniewicz, Ewa, 2007, The Middle Triassic scleractinia-like coral Furcophyllia from the Pamir Mountains, Acta Palaeontologica Polonica 52 (2), pp. 401-406 : 402-403

Furcophyllia shaitanica sp. nov.

Figs. 3A–C, F ; 4A .

Type material: Holotype, two succeeding transverse thin sections GID 20556/23. Paratype, fragmentary transverse thin section GID 20556/6.

Type locality: Valley of Šajtan river tributary of Kattamardžanaj river, the Peripheral zone in the SE Pamirs .

Type horizon: Upper Ladinian volcanogenic and clastic deposits in the upper Ladinian Šajtan suite of the Kattamardžanaj series .

Diagnosis.—Solitary with approximately 320 septa at the calicular diameter of 25 × 35 mm, in the both parameters similar to Furcophyllia septafindens ( Volz, 1896) , but differing from the latter in a thin structure of septal apparatus, and in the central axial pit, not in the form of linear calicular fossa.

Material.— Holotype and paratype only.

Measurements.—See Table 1.

Description.—The calice is oval with a slightly wavy or lobate outline of the calicular rim and a small axial pit. The wall is very thin, septothecal, probably covered by a thin epitheca. The septa are thin, straight or arcuate and arranged radially toward the axial pit. The septa branch in the same way as those in F. septafindens , some remain nonbranched, other intensively branch giving rise to new septa asymmetrically on both septal sides, and producing septal brooms ( Fig. 3A, F ). The septal brooms frequently are of a lense−like general shape. At the circumference, among septa producing septal brooms, there are quasi−systems composed of simple septa of the highest three or rarely four size orders well differentiated in length. The septal sides are densely covered with obtuse granulations that seem to be produced symmetrically on both septal sides and distributed in rows paralleling distal septal margin. The granulations reach far into the interseptal space, but the rows of adjacent septa rarely meet, suggesting their mutually alternating distribution. One of the sections shows a secondary calicular center in the vicinity of the axial pit of the adult corallum ( Fig. 3A, B ). This part of the corallum is re−crystallized, so the relationships between the two centers are not very clearly seen, but no septa are joining the centers. The new calice develops in the fan−like area limited by two septa of the adult calice. In the transverse section, the dissepiments are abundant, like those in F. septafindens and probably similarly extended ( Fig. 3E ).

Microstructure.—The septa are built of well delimited, rather isometric trabeculae that occupy the whole septal width ( Fig. 4A ). When observed in transverse section, each trabecula reveals a dark center corresponding to its Center of Rapid Accretion (CRA) and filled with diagenetically changed into opaque, calcitic deposit of the Center of Rapid Accretion (dCRA), surrounded by transparent sclerenchyme of its Thickening Deposit (TD); continuous accretion of dCRA results in formation of trabecular axis (terminology after Stolarski 2003). Lateral short offsets, provided each with a dark central axis, branch symmetrically from the main trabecula and form lateral septal granulations.

Remarks.—The differences between the species of Furcophyllia from the Dolomites and that from the Pamirs lie in the microstructural and morphological features. In F. shaitanica the trabeculae are thinner than in F. septafindens , the diameters being indicated by smaller distance between the centers CRA and smaller distances between lateral granulations ( Fig. 4A, B ). This results in smaller width of septal blades and higher septal density at the wall. But the structure of the axial part of the calice is by far more remarkably different, as the Pamirian species has a small, centered axial pit ( Fig. 3C ), while F. septafindens is characteristic for its long axial fossa ( Fig. 3D ). For the reason of radial distribution of septal apparatus, F. shaitanica corresponds more precisely to the models of furcated septal increase proposed in Stolarski et al. (2004), than in F. septafindens , having long fossa. F. shaitanica displays also a feature not presented by F. septafindens —the ability to form a secondary calicular center within the primary one. So, fixed polycentric conditions of corallum are not excluded in this species.

Figures

Fig. 3. Septal apparatus of Furcophyllia in transverse sections. A–C, F. Furcophyllia shaitanica sp. nov. Holotype, GID 20556/23, upper Ladinian of the SE Pamirs, Republic of Tajikistan. A. Corallum with two calicular pits: this of the adult calice and a secondary one of newly forming calice (arrows); two parallel septa (s) pass from the area of the axial pit of the adult towards the area occupied by the new pit, limiting this area from two sides. B. The secondary axial pit. C. The section situated more proximally in comparison with the previous one, cutting the middle calicular part; only primary axial pit is to be observed with its radial arrangement of septa, any rudiments of the secondary pit are lacking. F. Peripheral region of the corallum with well developed septal brooms. D, E. Morphology of Furcophyllia septafindens (Volz, 1896); IPUM DOL/610, middle Carnian, St. Cassian Beds, Forcella di Sett Sass, Dolomites, Italy. D. The section cutting obliquely the corallum at the level near by the calicular floor showing elongated calicular fossa. Compare the subparallel arrangement of septa in the central part of the calice with radial one in F. shaitanica sp. nov. E. Endotheca in longitudinal section: note steeply sloping down, very low and extended dissepiments.

Fig. 4. Septal microarchitecture and traces of microstructure of Furcophyllia in transverse sections. A. Furcophyllia shaitanica sp. nov. Holotype, IGD 20556/23, upper Ladinian of the SE Pamirs, Republic of Tajikistan. Densely arranged septa with minute lateral granulations; centers of rapid accretion (CRA) are marked by dark dots. B. Furcophyllia septafindens (Volz, 1896), IPUM DOL/610, middle Carnian, St. Cassian Beds, Forcella di Sett Sass, Dolomites, Italy. Septa with relatively thick lateral granulations.