Hexactinellida (Order: Reticulosa)
Protospongia is related to a primitive group of Hexactinellid sponges and resembles Diagoniella (Rigby, 1986). Hexactinellid sponges (glass sponges) have a skeleton composed of four to six-pointed siliceous spicules, they are considered to be an early branch within the Porifera phylum due to their distinctive composition.
Protospongia – from the Greek protos, “first,” and the Latin spongia, “sponge.”
hicksi – after H. Hicks, a palaeontologist who worked on fossil sponges.
Burgess Shale and vicinity: none.
Other deposits: Protospongia is widely known from the Cambrian to the Silurian in many siliciclastic and carbonate deposits.
Middle Cambrian, Bathyuriscus-Elrathina Zone to late Middle Cambrian Bolaspidella Assemblage Zone (approximately 505 million years ago)
Burgess Shale and vicinity: The Walcott Quarry on Fossil Ridge and several smaller localities on Mount Stephen.
Other deposits: P. hicksi occurs in the Middle Cambrian Marjum Formation (Rigby, 1966).
Brief history of research:
First described in 1888 by Hinde, this species was recognized from the Burgess Shale by Walcott in 1920. The genus was redescribed by Rigby in 1986 when reviewing the Burgess Shale sponges. In 2004, Rigby and Collins examined new material collected by the Royal Ontario Museum possibly attributable to this genus.
This sponge has been described only from fragments in the Burgess Shale so its shape and maximal size is unknown. However, specimens collected elsewhere show that this sponge had a globular to conical shape. The walls of this sponge were thin with a single layer of spicules. These spicules are known as stauracts, and differ from the normal six rayed spicules of the hexactinellid sponges in that they have two reduced rays which give them a distinctive cross-shape. Contrary to Diagoniella, the spicules are arranged parallel to the main axes of the sponge which gives it the distinctive square appearance. There are six orders of spicules present in the skeleton.
Protospongia is rare in the Walcott Quarry where it represents about 0.24% of the community (Caron and Jackson, 2008).
Protospongia would have lived attached to the sea floor. Food particles were extracted from the water as it passed through canals in the sponge’s wall.