Name: Hallucigenia
Phonetic: hal-lu-see-gen-ee-a.
Named By: Simon Conway Morris‭ ‬-‭ ‬1977.
Synonyms: Canadia Sparsa.
Classification: Animalia,‭ ‬Onychophora,‭ ‬Hallucigeniidae.
Species: H.‭ ‬sparsa‭ (‬type‭)‬,‭ ‬H.‭ ‬fortis.
Diet: Detritivore.
Size: 5‭ ‬to‭ ‬55‭ ‬millimetres long.
Known locations: Canada,‭ ‬British Columbia‭ ‬-‭ ‬Burgess Shale.‭ ‬China‭ ‬-‭ ‬Maotianshan Shale.
Time period: Early to Middle Cambrian.
Fossil representation: 109‭ ‬specimens.

       Hallucigenia was first identified as the Cambrian aquatic worm Canadia by Charles Doolittle Walcott in‭ ‬1911.‭ ‬However a study of the Canadia fossils by Simon Conway Morris in‭ ‬1977‭ ‬brought to light the discovery that the fossils did not represent the same creature.‭ ‬Because of its bizarre appearance of spikes and tentacles,‭ ‬Conway Morris gave the different individuals the name Hallucigenia because of their‭ ‘‬bizarre and dream-like quality‭’‬.‭ ‬However this realisation would be but the beginning of even more confusion about how it Hallucigenia lived.
       Fossils of Hallucigenia appear worm like with seven spines on one side,‭ ‬and seven pincer tipped tentacles on the other.‭ ‬Six of the tentacles match the spines for placement,‭ ‬the seventh however is forward.‭ ‬There are also three much smaller tentacles further along.‭ ‬On the ends of the main body were a blob on one end and a flexible tube on the other.‭ ‬Such a creature would be enough to make many palaeontologists give up and quit,‭ ‬but Morris persevered and worked out a conceivable reconstruction of the living creature.

       The first and original interpretation of Hallucigenia had it using its spines for walking.‭ ‬The flexible tail would reach down to the sea bottom and picking up morsels of food.‭ ‬The tail would then curl up and pass the morsel onto the first tentacle which would then pass it on to the next.‭ ‬The food morsel would then travel down the line of tentacles towards the‭ ‘‬blob‭’ ‬that was interpreted as being the head.
       There are a few problems with this interpretaion the first of which is that spikes,‭ ‬while possibly used for walking,‭ ‬would have been quite cumbersome.‭ ‬The second is that this method requires a lot of physical effort for feeding upon food sources that are possibly low in nutrients.‭ ‬Usually animals put as short a distance as possible between their mouths and their food source but in this reconstruction the distance is at its potential maximum.‭ ‬The third problem is that this method does not explain either the presence or function of the smaller tentacles at the base of the tail.
       A possible alternative to the above is if the spines were indeed placed at the bottom,‭ ‬could be that the spines were used to anchor Hallucigenia amongst rocks in the path of oceanic,‭ ‬or tidal currents.‭ ‬The tentacles would then drift upwards with their pincers catching food particles that were drifting in the current.‭ ‬The tentacles could then pass the food onto the mouth whichever end that may be,‭ ‬but if the mouth was on the tail and not the blob,‭ ‬then the tail could arc around to pick up the food morsels from the tentacles.‭ ‬Such a method would essentially see Hallucigenia living like a portable sea anemone.
       The second interpretation of Hallucigenia,‭ ‬and this is the one that is general accepted today,‭ ‬is to flip Hallucigenia over so that the spines point upwards and the tentacles are used for walking.‭ ‬This interpretation was proposed by Lars Ramskold and Hou Xianguang in‭ ‬1991,‭ ‬and is based upon fossils recovered from the Maotianshan shales of China.‭ ‬Not only does this see the spines in a defensive position,‭ ‬the tentacles are usually reconstructed to be in pairs.‭ ‬The blob was also interpreted as a stain caused by preservation,‭ ‬the claim based upon the observation that it is not present in all specimens.
       Although this is the most often represented reconstruction today,‭ ‬paired tentacles are not currently known in Hallucigenia fossils.‭ ‬The spines are also not considered by all to have been hard structures because they are never found on their own like the hard parts of other soft bodied creatures.‭ ‬The fossilised arrangement of the spines also only covers the main body.‭ ‬While this could theoretically deter suction feeders,‭ ‬other predators would have had quite a simple time avoiding them.
       The phylogenetic position of Hallucigenia is also strongly debated,‭ ‬and while many entries of Hallucigenia place within the Onychophora‭ (‬velvet worms‭)‬,‭ ‬not everyone is convinced that Hallucigenia belongs here.‭ ‬The possibility has even been raised that Hallucigenia may in fact be part of a larger animal,‭ ‬like how another Cambrian creature called Anomalocaris was first identified as a small shrimp until other body parts were pieced together to form the actual animal.‭ ‬There also what appears to be robust and gracile morphs of Hallucigenia which in‭ ‬2002‭ ‬were interpreted by Desmond Collins to represent male and female individuals.

Further reading
- A new metazoan from the Cambrian Burgess Shale of British Columbia. - Palaeontology 20: 623–640. - S. Comway Morris - 1977.
- The second leg row of Hallucigenia discovered. - Lethaia 25 (2): 221–4. - Lars - Ramsköld - 1992.
- A new species of Hallucigenia from the Cambrian Stage 4 Wulongqing Formation of Yunnan (South China) and the structure of sclerites in lobopodians. - Bulletin of Geosciences 87: 107–124. - M. Steiner, S. Hu, J. Liu & H. Keupp - 2012.
- Beyond the Burgess Shale: Cambrian microfossils track the rise and fall of hallucigeniid lobopodians. - Proceedings of the Royal Society B: Biological Sciences. 280 (1767): 20131613. - Jean-Bernard Caron, Martin R. Smith & Thomas H. P. Harvey - 2013.
- Hallucigenia's onychophoran-like claws and the case for Tactopoda. - Nature. 514 (7522): 363–366. - M. R. Smith & J. Ortega-Hernández - 2014.
- Hallucigenia's head and the pharyngeal armature of early ecdysozoans. - Nature. 523 (7558): 75–78. - Martin R. Smith & Jean-Bernard Caron - 2015.
- A hypothetical reconstruction of Hallucigenia. - PeerJ Preprints. 7: e27551v1 (1–10). - Christian McCall - 2019.


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