Sanctacaris

Sanctacaris is a Middle Cambrian Habellid[1] arthropod from the Burgess Shale of British Columbia. It was most famously regarded as a stem-group chelicerate, a group which includes horseshoe crabs, spiders and scorpions, although subsequent phylogenetic studies have not always supported this conclusion.[2] Its chelicerate affinities regain support in later observations,[3][1] alongside the reassignment of Habelia optata as a sanctacaridid-related basal chelicerate.[1]

Sanctacaris
Temporal range: Middle Cambrian
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Order: †Habeliida
Family: †Sanctacarididae
Genus: †Sanctacaris
Briggs & Collins, 1988
Species:
†S. uncata
Binomial name
†Sanctacaris uncata
Briggs & Collins, 1988

Sanctacaris specimens range from 46 to 93 mm in length.[4] The head bears five pairs of grasping appendages (corresponding to chelicerate's pedipalps and walking legs) and a sixth pair of posterior appendages (correspond to horseshoe crab's chilaria).[4] The grasping appendages each bear a antenna-like exopods.[3] There are 11 body segments, with the former 10 each bearing a pair of biramus appendage with flap-like exopod and reduced leg-like endopod. There is a broad, flat paddle-like telson.[4]

Originally Sanctacaris was called informally 'Santa Claws'. Its Latin name translates as "saintly crab".[5] Unlike most other Burgess forms, Sanctacaris is not present in Charles Walcott's 1909 quarry and was discovered at a different level by Desmond Collins in 1980–1981.[5]

References
  1. Aria C, Caron JB (December 2017). "Mandibulate convergence in an armoured Cambrian stem chelicerate". BMC Evolutionary Biology. 17 (1): 261. doi:10.1186/s12862-017-1088-7. PMC 5738823. PMID 29262772.
  2. Budd GE, Jensen S (May 2000). "A critical reappraisal of the fossil record of the bilaterian phyla". Biological Reviews of the Cambridge Philosophical Society. 75 (2): 253–95. doi:10.1017/s000632310000548x. PMID 10881389.
  3. Legg DA (December 2014). "Sanctacaris uncata: the oldest chelicerate (Arthropoda)". Die Naturwissenschaften. 101 (12): 1065–73. doi:10.1007/s00114-014-1245-4. PMID 25296691.
  4. Briggs DE, Collins D (August 1988). "A Middle Cambrian chelicerate from Mount Stephen, British Columbia" (PDF). Palaeontology. 31 (3): 779–798. Archived from the original (PDF) on July 16, 2011. Retrieved April 4, 2010.
  5. Briggs DE, Erwin DH, Collier FJ (1995). Fossils of the Burgess Shale. Washington: Smithsonian Institution Press. ISBN 1-56098-659-X. OCLC 231793738.
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