A new leptomitid-like sponge from the Early Ordovician of China with heteractinid spicules

A new sponge, Heteractenigma yui gen. et sp. nov., is described from the Corymbograptus deflexusBiozone (Floian) of the Ningkuo Formation in western Zhejiang Province, China. The tall, thin-walled species possessed unique features including a combination of robust longitudinal monaxons, fine sub-transverse monaxons, and minute hexactine and heteractine body wall spicules. The heteractine spicules have five rays in one plane, and closely resemble those of the problematic Burgess Shale sponge Petaloptyon danei. The monaxon organisation and body form, in contrast, accord with those of leptomitids. Although it is not currently possible to establish the precise relationships of this species, due to the major differences from other known taxa, it includes features characteristic of heteractinids, reticulosans and leptomitid protomonaxonids. This may indicate that the species belongs to the stem-group of either Porifera or Silicea. The unique architecture of the species also confirms that there remain large gaps in our knowledge of early sponges, even at high taxonomic level.