Lytvolasma aheimerensis, El-Desouky & Herbig & Kora, 2023

El-Desouky, Heba, Herbig, Hans-Georg & Kora, Mahmoud, 2023, Kasimovian (late Pennsylvanian) cornute rugose corals from Egypt: taxonomy, facies and palaeogeography of a cool-water fauna from northern Gondwana, Swiss Journal of Palaeontology (32) 142 (1), pp. 1-39 : 12-14

Lytvolasma aheimerensis n. sp.

( Fig. 7A–I ).

Derivation of the name: From the bearing rock unit “Aheimer Formation".

Holotype: Specimen RAh 2 , illustrated in Fig. 7A–I . Eight transverse thin-sections are available.

Material: In addition to the holotype, two moderately preserved paratypes with compressed to crushed calices and eroded apical ends (RAh 10 and RAh 113). Five 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 with thick wall, up to 2 mm thick. Cardinal septum shortened from early maturity. Counter septum elongated up to late maturity without forming a columella. It enters the free axial area with its rhopaloid end.

Description: External characters: Solitary, small, conicocylindrical corallites. The preserved parts of the three corallites ranges in length between 2 and 3 cm. Moderately preserved; their apexes and much of their early neanic stages are missing. Calices are deep. Growth lines, rugae, septal ridges and furrows are well-developed on the outer wall of the corallites. Rejuvenation is not common, only constrictions are visible ( Fig. 7A ).

Internal characters: The ontogenetically earliest growth stage available has 23 septa in 5.9 mm ( Fig. 7B, C ). Major septa are radially arranged. They are very thick and joined together in the centre forming a strong axial structure. The cardinal septum is somewhat thinner and the fossular break is noticeable. Further in the ontogeny, at a diameter of 8.8–13.3 mm with 24–26 septa ( Fig. 7D–H ), the septa become thinner gradually with maturity, and are more radially arranged. They are united near the axis with their rhopaloid ends, forming a stereozone with a free axial area. A strange attitude of one of the lateral cardinal septa is shown in Fig. 7G–I . It started to diminish gradually with maturity. This led to the reduction of the number of septa below the calice ( Fig. 7I ) to 25 septa. This attitude might be attributed to the rejuvenation took place in this part of the corallite. The cardinal fossula is slightly triangular and open adaxially. Counter septum is the longest with swollen end, invading the free axial area ( Fig. 7F ), and irregular in shape. Alar fossulae are not developed. The most adult stage, below the calice and the calice itself are compacted and the septa are somewhat deformed, the stereozone gradually diminishes and the septa retreat a little from the centre ( Fig. 7I ), the cardinal septum becomes distinctively shorter than the other major septa, whereas the counter is still long with thick rhopaloid end. The wall is thick (0.9– 2 mm) in all ontogenetic stages. Minor septa are absent. A white line in the midlines of the septa may indicate their original compound trabecular growth.

Discussion: The elongation of the counter septum makes this species similar to Monophyllum Fomichev, 1953 . It can be differentiated from Monophyllum in the shape of the cardinal fossula and the lack of the incipient columella formation in the calice. The current species differs from L. aucta Fedorowski, 1987 from the Pennsylvanian–Permian transition of southern Texas in the following:

• Number of septa are higher and diameter (n:d ratio) is larger in the present species.

• The wall of the current species is remarkably thicker.

• Minor septa are short and restricted to the corallite wall in the latest mature stages of L. aucta , whereas they are absent in the current species even in the last ephebic stage near the calice floor.

• The counter septum in the present species is longer, enters the free axial area, whereas it is only slightly longer than the other major septa in L. aucta .

The type species of the genus, L. asymetrica Soshkina, 1925 differs by the early appearance of free axial area in the holotype ( Fedorowski, 1987a, with comparisons to further similar specimens from different taxa) and the appearance of minor septa (Chwieduk, 2013), though n:d ratios are similar. L. aucta illustrated in Kora and Mansour (1991) (= L. paraaucta n. sp.) has smaller dimensions and a lower n:d ratio than the present species.

Figures

Fig. 7 Lytvolasma aheimerensis n. sp. A External view of the specimen RA (2), showing a straight corallite with partly eroded calice and non-preserved apical part, positions of thin-sections indicated.B–D Successive transverse thin-sections in the early preserved growth stages, shows very thick major septa joining together near the centre.The cardinal septum is deformed in D. E–G Successive thin-sections in the early mature stages show the formation of a stereozone with a free axial area,shortening of the cardinal septum with maturity and the longest counter septum with a rhopaloid end. H–I Two transverse thin-sections below the calice, deformed due to rejuvenation in H and lateral compaction in I. Scale bars: 2.5 mm, except A: 5 mm. Black dots indicate the positions of cardinal septum (below), counter septum (above) and the two alar septa