| Named By: | Simon Conway Morris in 1977 |
| Time Period: | Cambrian Stage 3-Middle Cambrian |
| Location: | Canada, British Columbia - Burgess Shale. China - Maotianshan Shale |
| Size: | 5 to 30 millimetres long |
| Diet: | Detritivore |
| Fossil(s): | 109 specimens |
| Classification: | | Animalia | Onychophora | Hallucigeniidae | |
| Also known as: | | Canadia Sparsa | |
Hallucigenia is a genus of Cambrian xenusiids known from articulated fossils in Burgess Shale-type deposits in Canada and China, and from isolated spines around the world. Its quirky name reflects its unusual appearance and eccentric history of study; when it was erected as a genus, the animal was reconstructed upside down and back to front. Hallucigenia is now recognized as a "lobopodian worm". It is considered by some to represent an early ancestor of the living velvet worms, although other researchers favour a relationship closer to arthropods.