New peri-Gondwanan occurrences of the Ordovician genus Diamphidiocystis (Echinodermata, Stylophora): implications for mitrocystitid palaeobiogeography and diversity

International audienceAbstract Anomalocystitid mitrates represent one of the most diverse and long ranging clade of stylophorans (Early Ordovician–Middle Devonian). Although they probably originated from a peri-Gondwanan stock of early mitrocystitids during the Floian, the fossil record of anomalocystitids in the Middle–Upper Ordovician of the Mediterranean Province remains extremely scarce and largely underestimated. The unusually shaped anomalocystitid genus Diamphidiocystis was originally described in the latest Katian–Hirnantian of North America (Illinois). However, earlier occurrences of this genus in the late Darriwilian of western France (Brittany) suggest a probable peri-Gondwanan origin. Based on new Middle to Late Ordovician material from the Anti-Atlas (Morocco), Bohemia (Czech Republic) and Brittany (France), all occurrences of Mediterranean Diamphidiocystis are considered as conspecific and formally described as D. regnaulti sp. nov. The palaeobiogeographical significance of Ordovician anomalocystitid mitrates is discussed