The Diploporita of the Oslo region, Norway

The Ordovician diploporite fauna from the Oslo Region is examined morphologically and taxonomically. The brachioles of Protocrinites are shown to be biserial. Pore-structures are described, including peripore connections and the structure of the skeletal mesh work. Internal morphological structures indicate a possible basal nerve ring and oral ring structures. Aspects of ontogeny and phylogeny dealt with include changes in plate number, an increased complexity of pore structures, and possibly an increased complexity of brachioles. A new family Parasphaeronitidae is described, comprising two new genera intermediate between Sphaeronitidae and Holocystitidae on the one hand and Aristocystitidae on the other. Fifteen taxa from three families are described, including three new genera (Tetreucystis, Parasphaeronites, and Pachycystis) and nine new species (Protocrinites rugatus, Haplosphaeronis bratterudensis, Eucystis langoeyensis, Tetreucystis kalvoeyensis, T. elongata, T. tetrabrachiolata, Sphaeronitidae sp. A, Parasphaeronites socialis, and Pachycystis norvegica). The stratigraphical and geographical distribution of genera and species within the Oslo Region is compared with the type of sediment in which they occur. Many genera have a relatively wide stratigraphical and geographical distribution but individual species are restricted. Morphological variation is relatively great and phylogenetic changes within the Norwegian diploporites are probably very complex.