Ultrastructure, taxonomy and affinities of some Ordovician and Silurian organic microfossils

The work present  the results of morphological and ultrastructural (TFM and SEM) studies on Ordovician and Silurian organic (non-calcareous) fossils among which representatives of scyphozoans, hydrozoans, pogonophorans and pterobranchs are recognized. A few forms of uncertain systematic position are also described. Scyphozoa: well preserved scyphothecae of Byronia robusta (Kozl.) are described along with ultrastructural observations made on other Byronia species. Part of the so-called dithecoid graptolites is recognized as colonial scyphopolyps. Hydrozoa: form, described by R. Kozlowski and A. Eisenack as hydroids are revised. The asrogenesis of Rhubdohydra tridens Kozl. is reconstructed. Two new taxa are designated. The periderm ultrastructure of five species is described and interpreted. Some forms known as dithecoid graptolites and the group Chaunogruptidae are recognized as colonial hydropolyps. Pogonophora: Beklemishevites grandis gen. et sp. n. is described. Tube ultrastructure is studied for two species revealing in one case the presence of a chitin-protein complex. Pterobranchia: forms described by R. Kozlowski are revised and a new taxonomy is proposed for Rhabdopleurida. Some forms classified previously as hydroids are identified as rhabdopleurids and five new taxa a redesignated. The astogenity of Rhabdopleurites primacvus Kozl. is reconstructed and new types of stolonal tubes (without zig-zag suture and fuselli) are described. The ultrastructure of cysts stolons and stolonal tubes is studied in several forms. A congenerity of Rhabdopleurites with so me forms described previously as tuboid or stolonoid graptolites and hydroids is suggested. Miscellanea: ulrastructure of five problemal microfossils a restudied. A few new taxa are described including two new genera.