Early Maastrichtian erect bryozoans from western Kazakhstan, with descriptions of two new species and the comparative internal morphology of some cheilostome genera

摘要

Erect cyclostome and cheilostome bryozoans are described for the first time from the lower Maastrichtian of the Aktolagay Plateau in western Kazakhstan. The studied bryozoan assemblage includes the cyclostomes Meliceritites cf dentiferus VISKOVA and ?Reteporidea sp., and the cheilostomes Rhagasostoma cf saltans (BRYDONE), Acoscinopleura beniamovski sp. nov. and Escharifora? invisibilia sp. nov. A combination of scanning electron microscopy and X-ray microtomography were used to characterize their external and internal morphologies. The comparative morphology of the studied cheilostome genera is discussed. The bryozoans belong to genera ubiquitous in the Maastrichtian of Europe and Central Asia. Moreover, R. cf saltans, A. beniamovski sp. nov. and E.? invisibilia sp. nov. have extensive geographical distributions.