Nalivkinia (Pronalivkinia) zvontsovi, F.Nikitin & E.Popov & G.Bassett, 2003

F. Nikitin, Igor, E. Popov, Leonid & G. Bassett, Michael, 2003, Late Ordovician brachiopods from the Selety river basin, north Central Kazakhstan, Acta Palaeontologica Polonica 48 (1), pp. 39-54 : 51-53

publication ID	https://doi.org/ 10.5281/zenodo.13285827
persistent identifier	https://treatment.plazi.org/id/0390B829-FFDC-FFBF-FCFB-1B1FFD147D6A
treatment provided by	Felipe
scientific name	Nalivkinia (Pronalivkinia) zvontsovi
status	sp. nov.

Treatment

Subgenus Pronalivkinia Rukavishnikova, 1977 Nalivkinia (Pronalivkinia) zvontsovi sp. nov.

Figs. 8 View Fig , 9A–F View Fig ; Tables 10, 11.

Derivation of name: After V. S. Zvontsov, Kazakhstanian geologist. Holotype: NMW 98.30 View Materials G.54, conjoined valves.

Type locality: Sample 5190, Shollakkarasu river, Selety river basin, Kazakhstan.

Type horizon: Ordovician, Tauken Formation.

Paratypes.—333 conjoined valves, six ventral and two dorsal valves.

Diagnosis.—Slightly dorsibiconvex shell about 90% as long as wide and 65% as thick as long, with a strongly uniplicate anterior commissure; dorsal median fold and ventral sulcus broad, occupying about 60% of maximum valve width; radial ornament of 24 to 30 rounded ribs with 4 to 8 ribs in the sulcus, 5 to 9 ribs on the fold.

Description.—Biconvex to slightly dorsibiconvex in mature specimens, subcircular to slightly transverse in outline.Ante − rior commissure uniplicate.Ventral valve moderately convex in transverse profile with maximum thickness between the umbo and mid−valve length.Beak slightly incurved.Del − thyrium open, triangular.Sulcus originates at about mid way between the umbo and mid valve length, deepening gradually anteriorly.Dorsal valve on average 84% as long as wide with a swollen umbonal region.Median fold originates between about 4 to 5 mm from the umbo, produced anteriorly as a high, semioval tongue.Radial ornament costate with 24 to 30 rounded ribs, including 4 to 8 ribs in the sulcus and 5 to 9 on the fold.

Ventral interior with strong teeth supported by thin dental plates, and a strong pedicle callist confined to the base of the delthyrial cavity.Ventral muscle field large, extending anteri − orly to the mid valve length with narrow, lanceolate adductor scars, completely enclosed by larger diductor scars.Dorsal valve with a narrow cruralium supported by a high median septum.Cardinal process simple, ridge−like.Crura divergent and directed anteriorly.Spiralial cones of up to 9 whorls, with dorso−medially directed apices and very short, posteriorly located and separated jugal processes.

Discussion.—This species differs from Nalivkinia (Pronalivkinia) rudis ( Rukavishnikova 1956) from the Upper Ordovician Dulankara Formation of the Chu−Ili Range, South Kazakhstan in having coarser radial ornament, a stronger dorsal median fold and ventral sulcus, and a thick shell which is usually about 60 to 70% as thick as long.In N. (P.) rudis the shell thickness is about half the sagittal length ( Popov et al. 2000).The number of ribs in N. (P.) rudis varies considerably, but is usually from 7 to 12, which is well above the range observed in N. (P.) zvontsovi .

Our new species differs from Nalivkinia ( Pronalivkinia ?) xichuanensis Xu, 1996 from the Upper Ordovician Shiyanhe Formation (Ashgill) of the Qinling Region, China in having coarser radial ornament with only up to 30 ribs, whereas in the Chinese species the number varies from 36 up to 48.

Occurrence.—Localities 397a, 550a, 780, 2523 and 5190.