© Royal Ontario Museum. Photo: Jean-Bernard Caron
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.
Protoprisma – from the Greek protos, “first,” and prisma, “prism.” This name refers to the early occurrence of this prismatic sponge.
annulata – from the Latin annulatus, meaning “ringed, or circular.” The name makes reference to the annulated growth form of this species.
Burgess Shale and vicinity: none.
Other deposits: none.
The Tulip Beds (S7) on Mount Stephen and the Raymond Quarry on Fossil Ridge.
Ribgy and Collins described this genus in 2004 based on material collected by the Royal Ontario Museum.
This sponge has an elongate annulated shape with several branches, which give it a hand-like appearance. Each branch has vertical angular ridges which results in a prismatic cross section. The ridges and the troughs between them are composed of fine hexactine spicules, cross-connected by horizontal strands that thatch the skeleton together. The type specimen is almost complete at 15 cm tall and shows that all of the branches originate from a central point at the base. The base of the sponge would have had an attachment structure to keep the sponge anchored in the sediment surface. As neither of the two specimens recovered are complete, it is not known what the top of this sponge would have looked like.
Protoprisma is known only from two specimens, one collected from the Tulip Bed (S7) locality on Mount Stephen and one from the Raymond Quarry on Fossil Ridge.
Protoprisma would have lived attached to the sea floor. Particles of organic matter were extracted from the water as they passed through canals in the sponge’s wall.
RIGBY, J. K. AND D. COLLINS. 2004. Sponges of the Middle Cambrian Burgess Shale and Stephen Formations, British Columbia. Royal Ontario Museum Contributions in Science (1): 155 p.