The internal morphology of Acoscinopleura Voigt, 1956 (Cheilostomata, Bryozoa) from the Campanian–Maastrichtian of Central and Eastern Europe

Abstract

Coscinopleurid cheilostome bryozoans are widespread in Latest Cretaceous sediments throughout the whole Boreal Chalk Sea. Despite having many polymorphs that can readily be distinguished, intraspecific plasticity is high and polymorph morphology shows only little variation over time. This significantly hampers taxon differentiation in coscinopleurids. In this study, we revise type material of three coscinopleurid species, Acoscinopleura foliacea (Voigt, 1930), A. fallax Voigt, 1956 and A. rugica Voigt, 1956, from the Maastrichtian of northern Germany using combined scanning electron microscopy and X-ray microtomography. The three species are morphologically very similar and were distinguished by the original author only in the shape and position of peripheral caverns inside their cryptocyst and in the position of vibracular polymorphs. X-ray microtomography allowed study of the internal morphology of the species and provided additional parameters that can be used for species differentiation. Septula, arch-like and channel-like cavities and microcavities could be identified inside the calcified walls. While the original identity of the type material of A. foliacea and A. rugica remains unchanged, the type material of A. fallax is shown to belong to three different species: A. fallax, A. occulta sp. nov. and A. dualis sp. nov. Additionally, hitherto-unstudied material from the late Campanian and Maastrichtian of northern Germany and Belarus is described as A. crassa sp. nov. and A. albaruthenica sp. nov.