The Early Sarmatian bryozoan Celleporina medoborensis sp. nov. from the Medobory reefs of western Ukraine (Central Paratethys)

Abstract

Moundlike, globular to hemispherical bryozoan colonies of Celleporina medoborensis sp. nov. are documented from the calcareous organodetrital, slightly marly facies of the Lower Sarmatian (Volhynian) serpulid-microbialite reefs, in the Polupanivka and Ditkivtsi quarries (Medobory Hills), located at the northeastern margin of the Carpathian Foreland Basin (Central Paratethys) in western Ukraine. The colonies of C. medoborensis are multilamellar, often with a subcircular hole and occur together with numerous cyclostome bryozoans (crisiids, tubuliporinids, branching colonies of entalophoroids) as well as schizoporellid and cryptosulid cheilostomes, accompanied by a few macro- and micro-fossil taxa. The combination of morphological characters such as: thick radial ribs in the pseudoporous, variably-shaped area of the ovicell, and one or two small adventitious oral, as well as large vicarious avicularia are the main characteristic features of species. The rich occurrence of the celleporiform colonies of C. medoborensis sp. nov. within the fine-grained calcareous sands of Polupanivka and Ditkivtsi suggests a shallow-water setting and high availability of soft substrates, probably dominated by calcareous algae upon which the bryozoans may have settled in the Medobory reef biota during the Early Sarmatian.