Middle Cambrian ‘Archaeocyathus’ from the Georgina Basin is an anthaspidellid sponge

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Abstract
Middle Cambrian (Ordian) fossils from the Ranken Limestone of the Georgina Basin previously referred to the genus Archaeocyathus were reputedly one of the last Australian occurrences of the phylum Archaeocyatha prior to its extinction. These fossils in fact represent the anthaspidellid sponge Arborella mors Gatehouse 1968, hitherto known only from isolated spicules, and are by far the earliest known examples of the family Anthaspidellidae. Rankenella nom. nov. is introduced for the primary homonym Arborella Gatehouse 1968. The genus confirms the preference of anthaspidellids for habitats in shallow-water reef and shelly facies evident in the known Ordovician occurrences of the group.