A candidate stem-group rossellid (Porifera, Hexactinellida) from the latest Ordovician Anji Biota, China

摘要

The living hexactinellid sponge family Rossellidae is characterised by hypodermal pentactine prostalia and reduction of hexactins to diactins in irregular choanosomal spicule strands. The fossil record of this family extends back to the Upper Cretaceous (?88 Ma), consistent with molecular-clock analyses that predict an origin at approximately 150 Ma. Herein we describe Matteolaspongia hemiglobosa gen. et sp. nov., one of the most abundant species in the latest Ordovician (444 Ma) Anji Biota of the Wenchang Formation, Zhejiang Province, South China. The biota preserves a relatively deep-water, sponge-dominated community from shortly after the end-Ordovician extinction. The new species described here possesses both hypodermal pentactine prostalia and a body wall including diactins, with an overall rossellid-like skeletal arrangement. However, differences from crown-group (extant) rossellids suggest either convergent evolution of the key characters, or a stem-group rossellid affinity for the new genus.