Bimineral Skeleton of Acoscinopleura crassa (Bryozoa, Cheilostomata) from the Maastrichtian of Germany Revealed Using X-ray Microtomography

The bimineral structure of the zooid walls of bryozoans Acoscinopleura crassa Koromyslova, Martha et Pakhnevich (order Cheilostomata) from the Maastrichtian of Germany has been revealed using X-ray microtomography. Presumably, the wall was partly calcitic, and partly aragonitic. One of the wall minerals contain one or more elements with a greater atomic number, which affected contrast of the skeleton layers. This resulted from either the replacement of one of the initial minerals by a contrast mineral, or from accumulation of trace elements. A similar process could have occured either during lifetime or posthumously. It was revealed that the bimineral skeleton of cheilostome bryozoans had already appeared in the Maastrichtian high-latitude seas.