Quick facts
| Known species | Hallucigenia sparsa |
|---|---|
| Group | Lobopodia, Panarthropoda |
| Age | Middle Cambrian, about 508 Ma |
| Locality | Burgess Shale, Canada |
| Length | About 1–3 cm |
| Limbs | Seven pairs of trunk lobopods |
| Defence | Seven pairs of dorsal spines |
| Evidence | Compressed soft bodies, claws and mouth region |
What can the fossils tell us?
Compression hid the second row of legs and made the rigid spines look like supports.
A dark blob once called the head was decayed material expelled from the gut.
They support relationship without making Hallucigenia a living velvet worm.
They do not distinguish carrion, prey and organic films.
Hallucigenia was a Cambrian lobopodian only a few centimetres long. Paired spines rose from its back, while soft legs with small claws extended below. Unusual compression first produced an upside-down reconstruction, but later specimens revealed the head, eyes, mouth and relationships of the animal.
Why the reconstruction was overturned
Charles Walcott described the fossil in 1911 as part of the polychaete worm Canadia. In 1977 Simon Conway Morris established Hallucigenia sparsa and placed it on the rigid spines, interpreting one visible row of soft projections as tentacles. The name reflected how implausible the resulting animal appeared.
Chinese lobopodians later showed that the paired soft projections were legs and that the spines belonged on top. On early flattened fossils the body overlapped the second row of legs. This was more than a casual observational error: two-dimensional compression concealed the symmetry of a three-dimensional animal.
Head, mouth and claws
Re-examination of H. sparsa identified an elongated head with a pair of simple eyes. A mouth at its end carried a ring of hardened elements, while needle-like teeth lined the front of the gut. The large dark stain formerly interpreted as a head proved to be gut material squeezed out during decay.
Each trunk leg ended in claws. Their nested construction resembles the claws of living onychophorans and supports placement of Hallucigenia among stem panarthropods. This is an anatomical relationship, not a claim that the Cambrian animal was a modern velvet worm.
Life on the seafloor
Hallucigenia walked over the marine bottom on seven pairs of soft trunk legs. The dorsal spines could deter attack, but connecting them to a particular predator such as Anomalocaris requires bite marks that are not currently available. Flexible front limbs may have helped bring food towards the mouth.
The exact diet is unpreserved. The oral ring and throat teeth show that it handled small soft food, but do not discriminate among carrion, tiny animals and organic coatings. Sharing a deposit with Wiwaxia does not by itself establish a feeding relationship.
The Palaeozoic Era guide gives the wider time setting, while the catalogue compares the first complete profiles in this collection.
Evidence, inference and reconstruction
| Direct | Body outline, paired spines, lobopods, claws, eyes and mouth region |
| Inference | Walking on the bottom and handling small soft food |
| Uncertain | Exact diet and the effectiveness of the spines |
| Reconstruction | Colour, gait, behaviour and a particular feeding scene |
Frequently asked questions
Did Hallucigenia really walk on its spines?
No. The spines stood on its back, while seven pairs of soft legs carried it over the bottom.
Where was its head?
At the elongated end bearing two simple eyes, a mouth and a tooth-lined front gut.
Was Hallucigenia a worm?
It was a lobopodian, an extinct panarthropod close to the early relatives of arthropods and onychophorans.
What did Hallucigenia eat?
Its mouthparts indicate small soft food, but the exact diet is unknown.