TAXONOMY, AND PALEOECOLOGY OF THE ORDOVICIAN EDRIOASTEROIDS OF THE BARRANDIAN AREA, CZECH REPUBLIC

Our understanding of Ordovician Isorophid edrioasteroids has been greatly expanded over the last 20 years by revision and descriptions of faunas from Laurentia and Perigondwana. However, one large gap in our understanding is the fauna from the Prague Basin. These edrioasteroids were described by Barrande (1887), and other than the description of two additional taxa, little has been done. The descriptions by Barrande were typical for the 19^th century, placing all taxa in the genus Agelacrinites, and describing them by gross morphology. Agelacrinites bellulus, described from internal molds of theca, is the senior synonym of A. latiusculus described from external molds. It is assignable to a new genus characterized by extremely wide, straight, and blunt ambulacra, and the absence of anterior shared cover plates. Agelacrinites bohemicus is the senior synonym of A. velatus (an internal thecal mold) and A. confertus (a specimen with a poorly preserved peripheral rim). This species is assignable to a new genus with strong affinities to Euryeschatia, and bears straight ambulacra with extremely high cover plates, and a separation of the hydropore oral and oral rise. Agelacrinites tener is an immature specimen assignable to Euryeschatia, bearing curved ambulacra. Agelacrinites simplex is assignable to Isorophusella bearing low, narrow, and straight ambulacra except for a slight curvature to ambulacrum C, and ambulacra cover plates arranged in a double biseries. Argodiscus hornyi Prokop 1965 is redescribed as a pyrgocystid from new material. The species is characterized by large, wide ambulacral cover plates that are arranged into chevrons. Argodiscus? rarus Plas and Prokop 1979 is assigned to Argodiscus and redescribed as a pyrgocystid. This species is known only from the holotype.

Barrandian edrioasteroids are all found in siliclastic sediments and utilized both shells of live hosts (trilobites and echinoderms) and skeletal debris (conulariids and cephalopods) for attachment. One species, Argodiscus hornyi is found exclusively attached to trilobites suggesting a commensal relationship. The species content is consistent with similarly aged faunas from Morocco consisting, of pyrgocystids, Euryeschatia, and Isorophusella, whereas Laurentian and Baltic faunas are dominated by Isorophids and edrioasterines.