Editing Hallucigenia (section)

==Description==
[[File:20210000 Hallucigenia diagrammatic reconstruction.png|thumb|left|Reconstructions of ''H. fortis'', ''H. hongmeia'', and ''H. sparsa'' in scale.]]

''Hallucigenia'' is a {{cvt|0.5|-|5.5|cm|in|frac=16}}<ref name="Liu-2014">{{Cite journal|last1=Liu|first1=Jianni|last2=Dunlop|first2=Jason A.|date=2014-03-15|title=Cambrian lobopodians: A review of recent progress in our understanding of their morphology and evolution|url=https://www.sciencedirect.com/science/article/pii/S003101821300285X|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|series=Cambrian Bioradiation|language=en|volume=398|pages=4–15|doi=10.1016/j.palaeo.2013.06.008|bibcode=2014PPP...398....4L|issn=0031-0182}}</ref><ref name="Smith-2015" /> long tubular animal with up to ten pairs of slender legs ([[lobopods]]).  The first 2 or 3 leg pairs are slender and featureless,<ref name="Liu-2014" /><ref name="Smith-2015" /><ref name="Siveter-2018">{{Cite journal|last1=Siveter|first1=Derek J.|last2=Briggs|first2=Derek E. G.|last3=Siveter|first3=David J.|last4=Sutton|first4=Mark D.|last5=Legg|first5=David|date=2018|title=A three-dimensionally preserved lobopodian from the Herefordshire (Silurian) Lagerstätte, UK|journal=Royal Society Open Science|volume=5|issue=8|pages=172101|doi=10.1098/rsos.172101|pmc=6124121|pmid=30224988}}</ref> while the remaining 7 or 8 pairs each terminate with 1 or 2 claws.<ref name="Steiner-2012" /><ref name="Smith-2015" /><ref name="Siveter-2018" /> Above the trunk region are 7 pairs of rigid conical sclerites (spines) corresponding to the 3rd&ndash;9th leg pairs.<ref name="Steiner-2012" /><ref name="Liu-2014" /><ref name="Smith-2015" /><ref name="Siveter-2018" /> The trunk is either featureless (''H. sparsa'')<ref name="Smith-2015" /> or divided by heteronomous annulations (''H. fortis''<ref name="HOU-1995">{{Cite journal|last1=HOU|first1=XIANGUANG|last2=BERGSTRÖM|first2=JAN|date=1995-05-01|title=Cambrian lobopodians-ancestors of extant onychophorans?|journal=Zoological Journal of the Linnean Society|volume=114|issue=1|pages=3–19|doi=10.1111/j.1096-3642.1995.tb00110.x|issn=0024-4082}}</ref> and ''H. hongmeia'').<ref name="Steiner-2012" /><ref name="Smith-2014" /> The "head" and "tail" end of the animal are difficult to identify; one end extends some distance beyond the legs and often droops down as if to reach the substrate. Some specimens display traces of a simple gut.<ref name="Smith-2015" />

Research in the mid-2010s clarified that the longer end is a head with anteroventral mouth and at least a pair of [[simple eye]]s.<ref>{{Cite journal|last1=Ma|first1=Xiaoya|last2=Hou|first2=Xianguang|last3=Aldridge|first3=Richard J.|last4=Siveter|first4=David J.|last5=Siveter|first5=Derek J.|last6=Gabbott|first6=Sarah E.|last7=Purnell|first7=Mark A.|last8=Parker|first8=Andrew R.|last9=Edgecombe|first9=Gregory D.|date=2012-09-01|title=Morphology of Cambrian lobopodian eyes from the Chengjiang Lagerstätte and their evolutionary significance|url=https://www.sciencedirect.com/science/article/pii/S1467803912000254|journal=Arthropod Structure & Development|language=en|volume=41|issue=5|pages=495–504|doi=10.1016/j.asd.2012.03.002|pmid=22484085|issn=1467-8039}}</ref><ref name="Liu-2014" /><ref name="Smith-2015" /> The shape of head differs between species – elongated in ''H. sparsa'', rounded in ''H. fortis'',<ref name="Liu-2014" /><ref name="Smith-2015" /> while those of ''H. hongmeia'' remain unknown.<ref name="Steiner-2012" /> At least in ''H. sparsa'', the head possesses radial teeth and [[pharyngeal teeth]] within the front of the gut.<ref name="Smith-2015">{{cite journal|last1=Smith|first1=Martin R.|last2=Caron|first2=Jean-Bernard|title=''Hallucigenia''{{'}}s head and the pharyngeal armature of early ecdysozoans|journal=Nature|date=2015|volume=523|issue=7558|pages=75–78|doi=10.1038/nature14573|pmid=26106857|bibcode=2015Natur.523...75S|s2cid=205244325|url=http://dro.dur.ac.uk/20476/1/20476.pdf}}</ref><ref>[[Rebecca Morelle|Morelle, Rebecca]], [https://www.bbc.com/news/science-environment-33262884 Face of bizarre sea creature Hallucigenia revealed], BBCNews, Science and Environment, 2015.06.25</ref>

''Hallucigenia''{{'s}} spines are made up of one to four nested elements. The spine surface of ''H. sparsa'' is covered in an ornament of minute triangular "scales",<ref name="Caron2013">{{cite journal |first1=Jean-Bernard |last1=Caron |first2=Martin R. |last2=Smith |first3=Thomas H. P. |last3=Harvey |title=Beyond the Burgess Shale: Cambrian microfossils track the rise and fall of hallucigeniid lobopodians |journal=Proceedings of the Royal Society B: Biological Sciences |volume=280 |issue=1767 |pages=20131613 |date=September 2013 |pmid=23902914 |doi=10.1098/rspb.2013.1613 |pmc=3735267}}</ref> while the spine surface of ''Hallucigenia hongmeia'' is a net-like texture of microscopic circular openings, which can be interpreted as the remains of Papillae.<ref name="Steiner-2012">{{cite journal |last1=Steiner |first1=Michael |date=2012 |title=A new species of ''Hallucigenia'' from the Cambrian Stage 4 Wulongqing Formation of Yunnan (South China) and the structure of sclerites in lobopodians |url=http://www.geology.cz/bulletin/fulltext/1280_Steiner.pdf |journal=Bulletin of Geosciences |volume=87 |issue=1 |pages=107–124 |doi=10.3140/bull.geosci.1280|doi-access=free }}</ref>