Abstract
As yet undescribed accumulations of shells of orthoconic cephalopods, which are in some aspects comparable to cephalopod limestones known from the Silurian and Lower Devonian of the Barrandian area and other regions of the world, occur in the Letná and Zahořany formations (middle Sandbian and lower Katian stages, Upper Ordovician, central Bohemia). These accumulated shells are often colonized by sessile organisms. Only a small proportion of these organisms could be attached to shells of alive cephalopods; the majority of them used empty shells as solid substrates. The most abundant epizoan is the cystosporate bryozoan of the genus Ceramopora that often overgrows the cephalopod shells extensively. Holdfasts of the genus Sphenothallus and problematic fossils assigned to the genus Conchicolites are common. Rarer epibionts include the bryozoan Spatiopora, the cystoid echinoderm Codiacystis and the brachiopod Ptychopeltis. Varying sizes of bryozoan colonies occurring on the same cephalopod shell point to several recurring attachment events, probably reflecting reproduction cycles.