Les Diastopora (Bryozoaires cyclostomes) néocomiensdu Jura suisse et français

Abstract

Under the name Diastopora are grouped tubularspecies hitherto assigned to the genera Diastopora and Entalophora. The diameter of the axial canal, a character used to separate the two genera, is partly correlated with the diameter of the stems and often with environmental factors. This character appears too variable; sometimes the stems of one colony would be placed two genera. The affinity of Diastopora with Mesentéripores is proved by the similarity of the three principal types of ovicells. The acknowledgement of three types of ovicells involve the distribution of the species in three groups. Perhaps, this is a first step towards the dismemberment of the genus Diastopora.Six species of Diastopora were found in the Neocomianof the Jura. Two are new: D. alata and D. compacta. The predominance of these species changes with stratigraphical position, paralleling lithofacies. D. tubulosa is dominant in the Lower Valanginian (hard or sandy bottom in agitated water?), but decreases in the Upper Valanginian (chiefly Calcaires à Alectryonia and marls rich in fragments of bivalve shells; shelly, sandy bottom with little mud) where D. alata becomes dominant. Finally, Diastopora with perforated ovicells (D. brunsvicensis, D. canaliculata, D. salevensis appear and replace the previous species during the Upper Valanginian and Lower Hauterivian, with expansion of the grey marl facies (muddy and deeper bottom?).