Demospongea (Order: Monaxonida)
Choia belongs to an early branch of siliceous sponge, the protomonaxonids at the base of the Demospongea (Rigby, 1986). Demosponges, the same group that are harvested as bath sponges, represent the largest class of sponges today.
Choia – derivation unknown, but probably from the Spanish word cholla referring to spiny cacti of the genus Opuntia which resembles the sponge Choia in shape and spiny elements.
carteri – in honor of H. J. Carter, a famous nineteenth century hexactinellid sponge specialist.
Lectotypes –USNM66482 (C. carteri),USNM66487 (C. ridleyi), in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA. (C. hindei, type and repository information unknown.)
Burgess Shale and vicinity: C. ridleyi (Walcott, 1920) from the Walcott Quarry; C. hindei (Dawson, 1896) from the Raymond Quarry.
Other deposits: C. utahensis (Walcott, 1920) from the Middle Cambrian Wheeler and Marjum Formations in Utah (Rigby et al., 2010); C. xiaolantianensis from the Lower Cambrian Chengjiang biota (Hou et al., 1999), C. sp. from the same formation near Haikou, Yunnan Province (Luo et al., 1999); and C.? sriata from the Lower Cambrian Hetang Formation, Anhui Province (Xiao et al., 2005). Choia is also known from the Ordovician of Morocco (Botting, 2007).
Middle Cambrian, Bathyuriscus-Elrathina Zone to late Middle Cambrian Bolaspidella Assemblage Zone (approximately 505 million years ago).
Burgess Shale and vicinity: The Walcott and Raymond Quarries on Fossil Ridge. The Collins Quarry and Trilobite Beds on Mount Stephen.
Other deposits: C. hindei (Dawson, 1896) from the Ordovician of Quebec at Little Métis to the Middle Cambrian Burgess Shale; C. carteri, C. hindei from the Middle Cambrian Wheeler and Marjum Formations in Utah (Rigby et al., 2010).
Brief history of research:
Choia was first described by Walcott (1920) based on specimens from the Burgess Shale, Utah and Quebec. The material from the Burgess Shale was re-examined in detail by Rigby (1986) and Rigby and Collins (2004).
Choia carteri consists of a flattened elliptical disc, up to 2 cm in diameter (5 cm including the long spicules), formed by fine radiating spicules from which stronger and long spicules up to 30 mm in length radiate. Other species differ in size and spine coarseness. C. ridleyi is generally smaller (less than 1.5 cm) and C. hindei larger (up to 8 cm).
Choia is not common in the Walcott Quarry where it represents only 0.2% of the Walcott Quarry community (Caron and Jackson, 2008). Only one specimen of C. hindei is known from the Burgess Shale (Rigby and Collins, 2004).
The sponge was not anchored to the sediment, but simply sat unattached on the sea floor. The long spicules are interpreted to have maintained the sponge above the sediment-water interface. Particles of organic matter were extracted from the water as they passed through canals in the sponges wall.