Ratcliffespongia Rigby, 1969

Beresi, Matilde Sylvia, Botting, Joseph P., Palafox, Juan J. & Buitrón Sánchez, Blanca E., 2017, New reticulosan sponges from the middle Cambrian of Sonora, Mexico, Acta Palaeontologica Polonica 62 (4), pp. 691-703 : 693-694

Genus Ratcliffespongia Rigby, 1969

Type species: Ratcliffespongia perforata Rigby, 1969 ; lower part of the middle Cambrian Marjum Formation ; Utah, USA .

Species included: The type species, Ratcliffespongia arivechensis sp. nov. and Ratcliffespongia multiforamina Wu, Yang, Jannussen, Steiner, Yang, and Zhu, 2005 from early Cambrian Huangbailing Formation of southern Anhui, South China ( Wu et al. 2005) and R. freuchenensis Botting and Peel, 2016 , from the early Cambrian of northern Freuchen Land, Greenland.

Remarks.— Ratcliffespongia has a complex taxonomic history, due to confusion by Rigby and Church (1990) over the nature of the type material of Rigby (1969), which they considered a decorticated outer layer of the bi-layered Hintzespongia Rigby and Gutschick, 1976 . This view was further promulgated by Finks and Rigby (2004). The issue was discussed by Botting and Muir (2014) and Botting and Peel (2016), with the result that R. wheeleri Rigby and Church, 1990 was reassigned to Hintzespongia , and the genus Ratcliffespongia retained for the type species and others. Differences between the relevant genera and species are explained in the species discussion below.

Other parietal gap-bearing taxa from the Burgess Shale-type faunas include Stephenospongia Rigby, 1986 , assigned to the Hintzespongiidae ( Finks and Rigby 2004) and known from fragments only. It is a thin-walled sponge that can be distinguished by its variably sized (often bisected) and orthogonally arranged parietal gaps, by the large size of the spicules relative to the parietal gaps and the development of vertical and horizontal skeletal bundles between the gaps. Stephenospongia has also been reassigned to the family Hintzespongiidae ( Finks and Rigby 2004; Rigby and Collins 2004), but this appears to be unwarranted given the absence of any evidence for a secondary skeletal wall, and differences from Hintzespongia in the preserved skeletal organisation.

The new material described here shows a simple, thin skeletal layer, with stauractines surrounding prominent parietal gaps, and without any dermal layer covering the openings. These features are shared with described species of Ratcliffespongia . There are small/slight differences between the species of Ratcliffespongia in the size and orientation of skeletal gaps, and differences in spiculation ( Botting and Muir 2014), but the structure is fundamentally different to the double layer of Hintzespongia and allies. For these reasons, we prefer to leave the family-level assignment of Ratcliffespongia open.

Stratigraphic and geographic range.— Recognised from the early Cambrian of China and Greenland, and the middle Cambrian of the Marjum and Weeler formations of Utah, USA, and Sonora, Mexico (this paper).