Parastrophina Schuchert and LeVene, 1929

Jin, Jisuo & Popov, Leonid E., 2008, A new genus of Late Ordovician-Early Silurian pentameride brachiopods and its phylogenetic relationships, Acta Palaeontologica Polonica 53 (2), pp. 221-236 : 225-226

Genus Parastrophina Schuchert and LeVene, 1929 Parastrophina portentosa (Nikitin and Popov in Nikitin et al. 1996)

Figs. 4 , 5 .

1996 Parastrophinella portentosa Nikitin and Popov in Nikitin et al. 1996: 91, figs. 5C, 6A–K.

Type material: Holotype, CNIGR 28 /12888, conjoined shell.

Type locality: Sample F−1014, Sortan−Manai , northern Betpak−Dala desert, Central Kazakhstan .

Type horizon: Upper Ordovician , lower Katian, Dulankara Regional Stage .

Material.— Paratypes, NMW 98.351 – 383 , total of 32 complete shells, same locality and stratum .

Diagnosis (emended herein).—Shell subpentagonal, dorsibiconvex, asymmetrical, with sigmoidal anterior commissure; ventral sulcus and dorsal fold originating at 7 mm or more from apex; costae subangular, 5–12 per valve, present in shells larger than 11 mm long. Spondylium V−shaped in transverse cross section, supported by medium septum along its entire length; septalium narrow, usually asymmetrical in cross section, supported by low median septum.

Discussion.—The species was initially thought to have a sessile septalium and assigned to Parastrophinella ( Nikitin et al. 1996) . Subsequent examination of paratypes by detailed serial sectioning shows that the species invariably possesses a low dorsal median septum that supports a septalium. Thus, the species is regarded herein as an aberrant form of Parastrophina , characterized by an asymmetrical shell and sigmoidal anterior commissure ( Fig. 4 ), unlike other species of the genus. Its dorsal cardinalia are similar to those of typical Parastrophina except for its asymmetrical cross section ( Fig. 5 ). In Parastrophina iliana Popov, Cocks, and Nikitin, 2002 , from the Upper Ordovician Anderken Formation of the Chu−Ili Range, the adult shells also show a tendency towards an asymmetrical anterior commissure, but their ventral sulcus and dorsal fold are well defined and the anterior commissure retains its uniplicate character.

Figures

Fig. 4. Pentameride brachiopod Parastrophina portentosa (Nikitin and Popov in Nikitin et al. 1996), Upper Ordovician, Dulankara Regional Stage, sample F−1014, Sortan−Manai, northern Betpak−Dala desert, Central Kazakhstan. A. NMW 98.28G.351, paratype, dorsal (A1), ventral (A2), anterior (A3), and lateral (A4) views of asymmetrical shell. B. NMW 98.28G.352, paratype, dorsal (B1), ventral (B2), lateral (B3), and anterior (B4) views. C. NMW 98.28G.353, paratype, lateral (C1) and anterior (C2) views of smooth, asymmetrical shell. D. NMW 98.28G.354, paratype, dorsal (D1), ventral (D2), lateral (D3), and anterior (D4) views of asymmetrical, juvenile shell.

Fig. 5. Transverse serial sections of two paratype specimens of Parastrophina portentosa (Nikitin and Popov in Nikitin et al. 1996), Upper Ordovician, Dulankara Regional Stage, sample F−1014, Sortan−Manai, northern Betpak−Dala desert, Central Kazakhstan. A. NMW 98.28G.383, juvenile specimen. B. NMW 98.28G.377. Numbers indicate distances from apex.