Sanctacaris is a Middle Cambrian habeliid arthropod from the Burgess Shale of British Columbia. It is currently considered to be one of the oldest relatives of chelicerates.
Discovery and etymology
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. The generic name "Sanctacaris " is a compound of the Latin words "sanctus" (saint or sacred) and "caris" (meaning crab or shrimp, a common suffix used in aquatic arthropods). The head bears a pair of eyes, as well as five pairs of biramous (two branched) appendages, the lower/inner branch of which (the endopods) comprise grasping appendages which bear spines primarily on their outer segments.<sup>Additional file 1</sup> The grasping head endopod appendages are each associated with a corresponding antenna-like exopod (outer branches). Based on Habelia, the head may have borne seven limb pairs in total, but these may be obscured in fossils by being under the head shield. One additional head limb pair is known, posterior to the first five, which is short but elongate, and bears a brush of setae (hair or bristle like structures) at its tip. While in the original description by Briggs and Collins 1988 this was suggested to be the sixth pair of head appendages, Aria and Caron 2017 suggest that it corresponded to the endopod of the seventh head limb pair known in the closely related Habelia. Its chelicerate affinities have regained support in later studies,
See also
- Paleobiota of the Burgess Shale