Invertebrate epibionts on Ordovician conulariids from the Prague Basin (Czech Republic, Bohemia)

摘要

Approximately 4% of just over 5000 conulariids from ten Ordovician formations in the Prague Basin (Czech Republic) exhibit invertebrate epibionts and/or attachment scars. The commonest epibionts are craniid bra-chiopods followed by bryozoans and edrioasteroids, which are invariably articulated. Less abundant are monoplacophorans, Sphenothallus sp., ?Lichenocrinus sp., and an indeterminate invertebrate. Epibionts occur on Anaconularia anomala, Archaeoconularia, Conulariella sp., and Pseudoconularia grandissima, though predominantly on A. anomala and Archaeoconularia from open shelf deposits in the Upper Ordovician Letn5. and Zahofany formations, in which conulariids are substantially more abundant than in other formations. Epibionts on a particular conulariid belong to a single species or up to three species and major taxa. Except for monoplacophorans, epibionts occur on the external surface of the conulariids, in some cases with brachiopods, bryozoans, or edrioasteroids present on all four faces. Brachiopods and edrioasteroids present on all four faces show little variation between the faces in their size range. Also, brachiopods show apparent random trending of the antero-posterior axis, while edrioasteroids on some specimens of A. anomala and Archaeoconularia are preferentially centered on or near the facial midline. On schott-bearing specimens of A. anomala exhibiting brachiopods and/or edrioasteroids, these and other epibionts are absent on the schott. Bryozoans on some A. anomala and Archaeoconularia cover portions of all four faces and corners, and on two specimens of A. anomala the schott, too, is encrusted. A similar case involving edrioasteroids on Archaeoconularia sp. from the Upper Ordovician Upper Tiouririne Formation of Morocco is documented.