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]