Ordovician receptaculitids from California and their significance



Well preserved receptaculitids from the Middle Ordovician in the Grapevine Mountains of Eastern California have been collected and studied. These highly variable specimens are regarded as intrapopulational variants of one species. This variation is due to differences in the microenvironment and to the occurrence of individuals at various stages of growth. These specimens are assigned to Ischadites mammillaris (Walcott 1884).This species differs from the similar species of Ischadites and Receptaculites in the following features: (1) small, numerous outer plates; (2) interlocking rays between the elements; and (3) curved and bifurcated inner shafts. Ischadites mammillaris is described and its morphology is compared to that of sponges and dasycladacean algae. Recent algal interpretations that regard the closed extremity of the receptaculitid as the growing end are believed to be incorrect. It is concluded that Ischadites mammillaris as well as other similar receptaculitids should retain their tentative alignment with the Porifera.