The head has a mouth opening at the anterior end and a pair of eyes (simple visual organs, not compound eyes) on the dorsal side 3). Three pairs of appendages on the neck are nearly equal length with the fourth through seventh appendages, but thinner than the others 3).
Presumably, Hallucigenia lived on the seafloor or on the surface of sponges, preying on those sponges, or was a scavenger, feeding on dead animals 2).
Hallucigenia is considered a stem group of the modern onychophoran, but its exact phylogenetic position has not yet been determined 2), 3).
Since Hallucigenia sparsa has a bizarre shape and its available specimens are rare, generic name "Hallucigenia" is derived from the Latin "hallucinatio" (wandering in the mind) and specific name "sparsa" from "sparsu" (rare) 2).
Hallucigenia was described at the first time in 1911 as the annelid polichelata by Walcott who discovered many of the Cambrian animal fossils 1), 2). After that, it has re-described by Conway Morris, but its relationship was still unknown and the anatomical interpretations on both of the dorso-ventral and the antero-posterior orientations were reversed 2).
- Conway Morris S (1977) A new metazoan from the Cambrian Burgess Shale of British Columbia. Palaeontology 20(3):623–640.
- Hallucigenia sparsa - The burgess Shale (Royal Ontario Museum).
- Smith M, Caron J (2015) Hallucigenia's head and the pharyngeal armature of early ecdysozoans. [abstract] Nature 523, 75–78. (DOI:10.1038/nature14573). (The full-text was referred to CORE.)