Lytvolasma paraaucta El-Desouky & Herbig & Kora 2023, n. sp.

Lytvolasma paraaucta n. sp.

(Fig. 8A 1–A 5, B 1–B 5, 12A).

1991 Lytvolasma aucta Fedorowski, 1987.- Kora and Mansour, figs. 2 c1, c2.

1991 Bradyphyllum cf. bellicostatum Grabau, 1928.- Kora and Mansour, figs. 2 b1, b2.

2001 Lytvolasma —Fedorowski and Bamber, p 48.

Derivation of the name: From the Greek “ para ” for resemblance to the species “ aucta ”.

Holotype: Specimen RAh 54, illustrated in Fig. 8A 1–A 5. Four transverse thin-sections are available.

Material: In addition to the holotype, four moderately preserved corallites with compressed calices and occasionally preserved apical part (RAh 19, RAh 74 and RAh 81); collected from the basal shales of the lower member of the Aheimer Formation. Eight transverse thin-sections are available. They are collected from the basal shales of the lower member of the Aheimer Formation.

Type locality: Eastern cliffs of the Northern Galala plateau (Lat. 29° 28 ′ 21 ″ N and Long. 32° 27 ′ 38 ″ E), northern Eastern Desert, western side of the Gulf of Suez, Egypt.

Type horizon: Basal shales of the lower member of the Aheimer Formation; Upper Pennsylvanian (Kasimovian).

Diagnosis: Lytvolasma having maximum n:d ratio 26:11.5. Major septa frequently thickened in all quadrants to make a stereocolumn that opens in the cardinal quadrants, that changes to half aulos in the counter quadrants with maturity. Cardinal septum is short within the fossula.

Description: External characters: Corallites are small, up to 3 cm long. The external wall is ornamented by septal furrows and fine concentric growth lines in the holotype specimen (Fig. 8A 1), in other paratypes the corallites are enclosed in mud and do not show any septal furrows (Fig. 8B 1). Calices either eroded or crushed and compressed (Fig. 8A 1). Two of the specimens with their apexes preserved. Two shallow constrictions are visible below the calicinal part in the holotype specimen. Constrictions are also observed in the apical part.

The following description refers mostly to the holotype (RAh 54).

Internal characters: The ontogenetically earliest preserved part has 18 septa in 4 mm of corallite diameter (Fig. 8A 2). At this stage major septa show irregular zaphrentoid arrangement. They are thick, among them only the cardinal is thinner, whereas the counter is thicker with rhopaloid ending. The cardinal fossula is noticeable with long cardinal septum that fuses with the other major septa making a dense stereocolumn in the centre, that opens in the cardinal quadrants. Minor septa are absent in this stage (see also Fig. 8B 2). The subsequent section made at a diameter of 7 mm shows 23 septa which are radially arranged (Fig. 8A 3). Their inner ends are rhopaloid and form a stereocolumn in the corallite centre. The cardinal fossula is slightly key-hole to subtriangular in shape and open adaxially (Fig. 8A 3, B3–B 4), with the cardinal septum thinner and slightly shortened.

The subsequent mature section is made beneath the calice floor (Fig. 8A 4). The corallite in this part is laterally compressed and almost half of the septa are broken and deformed. At this stage of maturity, the deformed cardinal fossula is bordered by a half aulos in counter quadrants. Major septa are almost radially arranged and are 24 in number. Cardinal septum is short within the fossula. Minor septa are rudimentary. They appear as small triangular spikes along the relatively thin epitheca. The last section within the compressed calice (Fig. 8A 4) is filled with mud and shows short major septa and underdeveloped minor septa. At a diameter of 11.5 mm of the paratype specimen (RAh 19), more or less at the base of the calice (Fig. 8B 5) the septal ends are free leaving a free axial area with a short cardinal septum and a relatively longer counter septum than the adjacent septa. The counter septum, always a little longer and/or slightly thicker than other major septa, a character clearly evident in the paratype specimen (Fig. 8B 3–B 5).

Discussion: Lytvolasma paraaucta n. sp. was illustrated by Kora and Mansour (1991; Fig. 2 c 1, c 2). Based on one transverse section in the mature part of the corallite and a longitudinal section, they assigned their specimen to L. aucta Fedorowski, 1987. Due to the lack of description and additional illustrations of younger ontogenetic stages Fedorowski and Bamber (2001) accepted this identification only at a generic level. We also include Bradyphyllum cf. bellicostatum Grabau, 1928 briefly described and figured by Kora and Mansour (1991, p. 599, Fig. 2 c 1c 2) in our new species. Additional transverse thin-sections from the youngest stages clearly confirm the difference of the Egyptian specimens from L. aucta by the following characters:

• Lytvolasma paraaucta n. sp. has higher n:d ratios than the holotype of L. aucta (Fig. 12A). Nevertheless, L. aucta paratypes can reach a higher n:d ratio up to 22:9.

• The septal ends in the Egyptian species are thickened in contiguity to form a stereocolumn that is open towards the cardinal fossula, whereas in L. aucta, the septal ends are free or form a half aulos only in the counter quadrants.

Lytvolasma paraaucta n. sp. differs from L. canadense Fedorowski and Bamber, 2001 from the Middle Permian of the Canadian Arctic Archipelago, in having an unremarkable counter septum, which is elongated in L. canadense in the calice and below its bottom. It also slightly differs by its n:d ratio in the ephebic stage near the calice floor (24:12? vs. 26:12.6; Fig. 12A). The same case is for the Egyptian Lytvolasma cf. canadense.

In relation to L. asymetrica Soshkina, 1925, described from the Early Permian (Sakmarian) of Spitsbergen by Chwieduk (2013), the current new species has slightly similar n:d ratio in the mature stage below the calice (24:12? vs. 23–26: 8–14 in L. asymetrica; Fig. 12A). However, in L. asymetrica the inner ends of major septa join to form a quite irregular, incomplete aulos that opens on the alar septum sides throughout most of ontogeny; whereas in the current species a stereocolumn is developed through most of its ontogeny and in the mature stage, the thickened inner ends of the septa form an aulos that opens on the cardinal side (Fig. 8A 3, A 4).