Pseudopholidops anteglacialis, Mergl, 2012

Mergl, Michal, 2012, Lingulate And Craniate Brachiopods From The Top Of The Králův Dvůr Formation (Latest Katian) And Their Contribution To Palaeogeography, Acta Musei Nationalis Pragae Series B 68 (1 - 2), pp. 35-46 : 39-42

Pseudopholidops anteglacialis sp. nov.

Text-fig. 3

H o l o t y p e: Ventral valve, internal mould, illustrat- ed in Fig. 3 I, J (PCZCU 1835).

T y p e h o r i z o n: Upper Katian, Králův Dvůr Formation, ‘Perník bed’.

T y p e l o c a l i t y: Praha – Řeporyje, a temporary outcrop.

E t y m o l o g y: Ante (Latin) – before, and glaciális (Latin) – glacial.

M a t e r i a l: Eighteen valves preserved as internal and external moulds in claystone (PCZCU 1826 to 1843).

D e s c r i p t i o n: Shell is small, biconvex, 2.1 mm wide in the largest collected specimen, having maximum width anteriorly to shell midlength.

Dorsal valve is elongate oval, 133 % as long as wide in specimens measured (n = 2), thick-walled posteriorly, but anteriorly having a comparatively thin shell wall. Sides and anterior margin are evenly curved. Apex is marginal. Limbus is prominent posteriorly and posterolaterally and rapidly weakens anteriorly. Anterior margin is without the limbus. Shallow incision is present on anterior edge of posteri- or limbus. Valve is moderately and evenly convex transversally and axially. Dorsal pseudointerarea is low anacline, with transversally striated surface. Dorsal visceral area is weakly impressed in posterior part of the valve, being some 40 % as wide as the valve, and anteriorly limited by the shell midlength. Paired anterior adductor scars are large, subtriangular, divided from each other by elongate subrectangular scars of brachial protractors. Posterior unpaired median scars extend significantly posteriorly from the visceral field. Posterior adductor and oblique internal muscle scars are undivided and weakly impressed.

Ventral valve is elongate-oval, moderately convex in transverse and axial profiles, deepest posteriorly, having gently evenly rounded sides and more rounded anterior margin. Valve is 117 to 140 % as long as wide (n = 12), with outline range from narrowly to broadly oval but it is difficult to distinguish the original variability due to deformation in the clayey shale. Broadly triangular low apsacline ventral pseudointerarea bears fine transverse striation. Apex is marginal, extended posteriorly. Apical angle is approximately 100°. Ventral limbus is tall and broad posteriorly and posterolaterally but vanishing anteriorly. Ventral visceral area is trapezoidal in outline, weakly impressed, some 40 % as wide as valve and extended into the valve midlength. Paired large anterior adductor scars are divided by a short tongue, which is the site of oblique internal muscle attachments.

Exteriors of both valves bear fine growth lines, which are at regular intervals extended into coarser concentric lamellae. There are 8 to 10 lamellae in large shells.

R e m a r k s: Apart from the absence of a ventral median ridge, the outline is consistent with attribution of the new species to Pseudopholidops BEKKER, 1921 . The type species P. scutellata ( BEKKER, 1921) figured by Popov and Holmer (2000) differs by more numerous growth lamellae and narrower limbus. The new species is very similar to Pseudopholidops stolleyana ( HUENE, 1900) from the Baltic area ( Huene 1900, Popov and Pushkin 1986). The only difference are weaker impressions of the muscle scars in P. stolleyana . The new material is described as a new species also due to a biological reason. Despite a distinct relationship between the Baltic and Bohemian shelly taxa in the late Katian, it is taxonomically related only at a generic or high- er level. There are no species common to both areas.

Sanxiaella RONG et CHANG, 1981 (in Chang 1981) is a suggested synonym for Pseudopholidops BEKKER, 1921 after Popov and Holmer (2000). Pseudopholidops partibilis ( RONG, 1979) , the type species of the invalid genus Sanxiaella , is not a well known species. This Chinese species has a smaller and more distinct visceral platform and its shell is less elongate in comparison with P. anteglacialis .

Pseudopholidops is a characteristic genus for the Hirnantia Fauna of China (Rong and Chang 1981), and has been also reported from the Hirnantia Fauna of Bohemia ( Mergl 1986). Sanxiaella sp. material from the Kosov Formation (Hirnantian) is poor ( Mergl 1986, Havlíček 1994a), but it seems that the Hirnantian species differs from the new species by a weaker posterior limbus, higher visceral platforms and a less extended posterior margin lacking a distinct pseudointerarea. Based on the last feature, Mergl’s (1986) Sanxiaella sp. is more related to the unnamed Hirnantian species of Pseudopholidops which was originally referred to Paracraniops by Bergström (1968).

O c c u r r e n c e: moderately frequent.

Only in the type locality where it is

Figures

Text-fig. 3. Pseudopholidops anteglacialis sp. nov., Králův Dvůr Formation, ‘Perník bed’, Praha-Řeporyje locality. Bar = 1 mm. A – Dorsal valve, internal mould, PCZCU 1843. B – Dorsal valve, internal mould, PCZCU 1840. C, K – Ventral valve, internal and external moulds, PCZCU 1831. D – Ventral valve, internal mould, PCZCU 1827. E – Dorsal valve, internal mould, PCZCU 1826. F – Ventral valve, internal mould, PCZCU 1830. G – Ventral valve, internal mould, PCZCU 1832. H – Dorsal valve, internal mould, PCZCU 1841. I, J – Holotype, ventral valve, internal and external moulds, PCZCU 1835. L – Exterior, external mould, PCZCU 1836.