Retiophyllia aranea, Roniewicz, 2011

Roniewicz, Ewa, 2011, Early Norian (Triassic) corals from the Northern Calcareous Alps, Austria, and the intra-Norian faunal turnover, Acta Palaeontologica Polonica 56 (2), pp. 401-428 : 414

Retiophyllia aranea sp. nov.

Fig. 4B .

Etymology: From Latin aranea , spider; referring to the thin plot of the skeletal elements.

Holotype: GBA 2009 /019/14 with thin sections.

Type locality: Austria, Northern Calcareous Alps, southern Dachstein Plateau, site ca. 50 m north−west of Feisterscharte.

Type horizon: Norian, Lacian 1, Epigondolella quadrata Conodont Zone ; light−grey Dachstein limestones.

Diagnosis.— Retiophyllia with about 50 septa at a diameter of 4 mm, flat calicular floor, and relatively large peripheral dissepiments.

Comparison.—The species differs from the congeneric species in thin, numerous septa at a small corallite diameter, and in zonation of the endotheca, with a ring of large dissepiments encircling the axial cavity with a calicular floor made of flat, tabuloid dissepiments. From the coral most similar in measurable features, R. paraclathrata Roniewicz in Turnšek (1997: 183, figs. A–H; with synonymy), the new species differs, beside the endotheca of a structure described above, in possessing finer septa. The corallites fork at an acute angle. It cannot be determined if apophyseal intercorallite connections are present.

Material.— The holotype and specimen GBA 2009 /019/15, with thin sections .

Measurements (in mm):

GBA d s sd/1 ed/3 Remarks 2009/019/14 4.0–4.5 41–47 4–5 10–14

adults 2009/019/15 4.0–4.5 40–60 4–5 –

Description.— Septa thin, differentiated into four size orders, arranged in adult forms into 9–10 systems. The S1 septa and S2 septa fusiform and exsert, the S1 septa reaching the axis, the S2 septa conspicuously shorter, the S3 septa of about half the length of the S1 septa. The S4 septa very short and variably developed: rare in the holotype colony but regularly distributed in the corallites of GBA 2009/019/15. In transverse sections, the septal flanks show rare, protruding granules. Endotheca abundant. At the zone of maximum thickness of fusiform septa, the endotheca is composed of a ring of convex, relatively large dissepiments; smaller dissepiments develop externally to that ring; horizontal, tabuloid dissepiments form a large and flat calicular floor. Wall thin. Corallum increasing by equivalent division of corallites, lacking constriction at the early stage of division, and with long−lasting connection between new corallites.

Stratigraphic and geographic range.— Austria: Northern Calcareous Alps, Dachstein Plateau, north of Feisterscharte, lower Norian, Epigondolella quadrata Conodont Zone. Slovenia: Northern Julian Alps, Lacian.

Figures

Fig. 4. Reimaniphylliid corals from vicinity of Feisterscharte, Austria, early Norian, Triassic. A. Retiophyllia sp.; GBA 2009/019/4g. Septal apparatus with + thick S1 septa, transverse section. B. Retiophyllia aranea sp. nov.; GBA 2009/019/14. corallites circular in section (B1) with a large axial space (B2); longitudinal/oblique section (B3) showing sub−horizontal, large dissepiments in the axial space, and longitudinal section of distal part of the corallite (B4) show− ing convex dissepiments at the periphery.C. Retiophyllia aff. fenestrata (Reuss, 1854); GBA 2009/019/11a, b. Corallites in transverse (C1) and longitudinal (C2) sections showing small number of septa and large dissepiments. D. Retiophyllia aff. tolminensis Turnšek, 1987; GBA 2007/152/3f. Corallite in transverse section showing zigzag septa. E. Retiophyllia vesicularis sp. nov.; GBA 2009/019/12g, c. Corallites in longitudinal (E1) and transverse (E2) sections; note large and convex dissepiments and irregular shape of septa. F–G. Craspedophyllia? sp. F. GBA 2009/019/16b; transverse sections with corallites showing rare, obliquely directed menianes. G. Zigzag traces of septal microstructure; GBA 2009/019/17a (G1), GBA 2009/019/17b (G2).