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Canadia spinosa; Temporal range: Middle Cambrian PreꞒ Ꞓ O S D C P T J K Pg N
	Fossil of Canadia spinnosa
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Annelida
Class:	Polychaeta
Genus:	†Canadia; Walcott, 1911
Species:	†C. spinosa
Binomial name
	†Canadia spinosa; Walcott, 1911

Canadia (meaning of Canada or after Canada) is a genus of extinct annelid worm present in Burgess Shale type Konservat-Lagerstätte. It is found in strata dating back to the Delamaran stage of the Middle Cambrian around 505 million years ago, during the time of the Cambrian explosion. It was about 3 centimeters (1.2 inches) in length. Charles Doolittle Walcott named Canadia in 1911 after Canada, the country from which its remains have been found. 28 specimens of Canadia are known from the Greater Phyllopod bed, where they comprise 0.05% of the community.^[1]

Description

With length up to 4.5 centimeters (1.8 inches),^[2] the animal's most notable feature is the many notosetae (rigid setae extending from dorsal branches of notopodia) along the back of the animal that are characteristic of polychaete worms. A 1998 paper suggested that it may have been iridescent due to the supposed presence of diffraction gratings,^[3] however other studies have interpreted these structures as internal microvilli.^[4]

Tentacles extended from the prostomium and may have served as sensory organs. The gut of Canadia was straight and had the ability to extend out of the body in the form of a proboscis, suggesting that the animal was carnivorous. This is further evidenced by the lack of sediments found in the gut that would be present in a benthic detritivore.^[5] Canadia is thought to have swum above the seafloor as a primary means of locomotion by beating its numerous notosetae.^[6]

It would also have had the ability to creep along the seafloor using the ventral counterpart of the notopodia, which are termed neuropodia (in reference to the proximity to the paired, ventral nerve cords characteristic of annelids).

Classification

There has been some debate as to the placement of Canadia within the Annelida phylum. Although it is commonly accepted to be within Annelida, it is uncertain how it relates to modern annelids. Most paleontologists agree that it belongs to the class Polychaeta due in part to the presence of Parapodium. It has been proposed to be a member of the order Phyllodocida along with Wiwaxia, another organism from the Burgess Shale. Both were placed in a new superfamily called Canadiacea, and were thought to be of closer relationship to each other than to modern annelids.^[7] However, Wiwaxia is no longer believed to have been an annelid and there is currently dispute as to whether or not Canadia should be classified as belonging to anything more derived than Polychaeta.^[2]

References

Parker, Steve. Dinosaurus: the complete guide to dinosaurs. Firefly Books Inc, 2003. Pg. 37

^ Caron, Jean-Bernard; Jackson, Donald A. (October 2006). "Taphonomy of the Greater Phyllopod Bed community, Burgess Shale". PALAIOS. 21 (5): 451–65. doi:10.2110/palo.2003.P05-070R. JSTOR 20173022.
^ ^a ^b Eibye-Jacobsen, D. (September 2004). "A reevaluation of Wiwaxia and the polychaetes of the Burgess Shale. Lethaia, v.37, no.3, p. 317-335
^ Parker, A. R. 1998. Colour in Burgess Shale animals and the effects of light on evolution in the Cambrian. Proceedings of the Royal Society of London Series B 265:967-972.
^ Parry, Luke; Caron, Jean-Bernard (2019-09-06). "Canadia spinosa and the early evolution of the annelid nervous system". Science Advances. 5 (9): eaax5858. doi:10.1126/sciadv.aax5858. ISSN 2375-2548. PMC 6739095.
^ "Paleobiology | Smithsonian National Museum of Natural History".
^ Conway Morris, S. (1979). "Middle Cambrian Polychaetes from the Burgess Shale of British Columbia". Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 285 (1007): 227–274. Bibcode:1979RSPTB.285..227M. doi:10.1098/rstb.1979.0006. JSTOR 2418139.
^ Butterfield, N.J., 1990b. A reassessment of the enigmatic Burgess Shale fossil Wiwaxia corrugata (Matthew) and its relationship to the polychaete Canadia spinosa Walcott. Paleobiology, v.16, no.3, p.287-303