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] There are 11 body segments, with the former 10 each bearing a pair of biramous appendages with flap-like exopod and reduced leg-like endopod.

[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] 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).

[4] The robust gnathobases, alongside the fact that fellow sanctacaridid Wisangocaris has been found with trilobite fragments in its stomach, has led to suggestions that Sanctacaris was durophagous, feeding on hard shelled organisms.