The oldest bifoliate cystoporate and two other bryozoan taxa from the Dapingian (Middle Ordovician) of north-western Russia

Abstract

Bryozoans from the Dapingian (Middle Ordovician) of the Baltic paleobasin remain poorly studied and their taxonomic composition is unclear. In this paper, three bryozoan taxa, a bifoliate cystoporate Planopora volkhovensis n. gen. n. sp., a trepostome Hemiphragma insolitum n. sp., and an esthonioporate Esthoniopora clara Koromyslova, are described from Dapingian deposits of an unusual clayey-calcareous Hecker-type mudmound on the right bank of the Volkhov River in Leningrad Oblast’, north-western Russia. Combined X-ray microtomography, scanning electron microscopy, and light microscopy of thin sections were used to characterize their morphology. Analysis of the stratigraphic distribution of early cystoporate bryozoans suggests that Planopora n. gen. is the oldest сystoporate bryozoan with an erect, bifoliate colony. The growth modes of these bryozoans are discussed. The colonies of P. volkhovensis n. gen. n. sp. and E. clara have an attachment structure, a holdfast, at their base, probably indicating their attachment to sponge spicules. The bryozoan H. insolitum n. sp. produced rod-like colonies, formed by overgrowing the problematic tubular fossil Sphenothallus Hall. It can be assumed that sponges with unfused siliceous spicules and individuals of Sphenothallus were numerous on the surface of the mudmound during its formation and provided a suitable substrate for settlement of bryozoan larvae. UUID: http://zoobank.org/5715872a-8c61-446e-9413-d713fdef1a08

Bryozoan fauna from the Kunda Stage (Darriwilian, Middle Ordovician) of Estonia and NW Russia

“…Separate bryozoan taxa were treated in various publications (e.g. Modzalevskaya 1953Modzalevskaya , 1986Lavrentjeva 1975Lavrentjeva , 1985Gorjunova & Lavrentjeva 1993;Fedorov et al 2017;Koromyslova & Fedorov 2021).…”