Sanctacaris


Sanctacaris is a Middle Cambrian Habellid 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. Its chelicerate affinities regain support in later observations, alongside the reassignment of Habelia optata as a sanctacaridid-related basal chelicerate.
Sanctacaris specimens range from 46 to 93 mm in length. The head bears five pairs of grasping appendages and a sixth pair of posterior appendages. The grasping appendages each bear a antenna-like exopods. 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.
Originally Sanctacaris was called informally 'Santa Claws'. Its Latin name translates as "saintly crab". 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.