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 cystoporatePlanopora volkhovensisn. gen. n. sp., a trepostomeHemiphragma insolitumn. sp., and an esthonioporateEsthoniopora claraKoromyslova, 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 thatPlanoporan. gen. is the oldest сystoporate bryozoan with an erect, bifoliate colony. The growth modes of these bryozoans are discussed. The colonies ofP.volkhovensisn. gen. n. sp. andE.clarahave an attachment structure, a holdfast, at their base, probably indicating their attachment to sponge spicules. The bryozoanH.insolitumn. sp. produced rod-like colonies, formed by overgrowing the problematic tubular fossilSphenothallusHall. It can be assumed that sponges with unfused siliceous spicules and individuals ofSphenothalluswere 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

中文翻译：

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俄罗斯西北部大坪期（中奥陶纪）最古老的双叶孢子虫和另外两个苔藓虫类群

波罗的海古盆地大坪阶（中奥陶统）的苔藓虫研究仍然很少，它们的分类组成也不清楚。在本文中，三个苔藓虫类群，一个双叶囊孢菌大白菜n. 将军 n. sp.，一个螺旋体独角仙n. sp.，和一个 esthonioporate尖孔虫Koromyslova，被描述于俄罗斯西北部列宁格勒州沃尔霍夫河右岸的一个不寻常的粘土-钙质赫克型泥丘的大坪阶沉积物中。结合 X 射线显微断层扫描、扫描电子显微镜和薄片的光学显微镜来表征它们的形态。早期囊孢苔藓虫的地层分布分析表明，扁平孔虫n. 将军 是最古老的 сystoporate 苔藓虫，具有直立的双叶菌落。讨论了这些苔藓虫的生长模式。的殖民地磷.沃尔霍文斯n. 将军 n. sp。和乙.克拉拉在它们的基部有一个附着结构，一个固定器，可能表明它们附着在海绵骨针上。苔藓虫H.孤零零n. sp。产生棒状菌落，由过度生长有问题的管状化石形成蝶体大厅。可以假设具有未融合硅质骨针的海绵和个体蝶体在其形成过程中在泥丘表面有许多，并为苔藓虫幼虫的沉降提供了合适的基质。UUID：http://zoobank.org/5715872a-8c61-446e-9413-d713fdef1a08