Editing Hallucigenia (section)

==History of study==
[[File:20210917 Hallucigenia sparsa interpretations.png|left|thumb|Various interpretations of ''Hallucigenia sparsa'' throughout the history of study]]

''Hallucigenia sparsa'' was originally described by [[Charles Doolittle Walcott|Charles Walcott]] as a species of the [[polychaete worm]] ''[[Canadia (annelid)|Canadia]]''.<ref>WALCOTT, C. 1911. [https://repository.si.edu/handle/10088/34820 Cambrian Geology and Paleontology II. Middle Cambrian annelids]. Smithsonian Miscellaneous Collections, 57(5): 109–145.</ref> In his 1977 redescription of the organism, [[Simon Conway Morris]] recognized the animal as something quite distinct, for which he proposed the name ''Hallucigenia'' because of the "bizarre and dream-like appearance of the animal." No specimen was available that showed both rows of legs, so Conway Morris reconstructed the animal walking on its spines, with its single row of legs interpreted as tentacles on the animal's back. A dark stain at one end of the animal was interpreted as a featureless head. Only the forward tentacles could easily reach to the "head", meaning that a mouth on the head would have to be fed by passing food along the line of tentacles. Conway Morris suggested that a hollow tube within each of the tentacles might be a ''mouth''.<ref name=ConwayMorris1977 /> This raised questions, such as how it would walk on the stiff legs, but it was accepted (with reservations) as the best available interpretation.<ref name="Gould">{{cite book |last=Gould |first=Stephen Jay |author-link=Stephen Jay Gould |title=Wonderful life: the Burgess Shale and the nature of history |publisher=W.W. Norton |location=New York |year=1989 |pages=154–157 |isbn=978-0-393-02705-1 |url-access=registration |url=https://archive.org/details/wonderfullifebur00goul }}</ref>

[[File:HallucigeniaSparsa-ROM-June11-10.jpg|thumb|Specimen with obvious spines]]

An alternative interpretation considered ''Hallucigenia'' to be an appendage of a larger, unknown animal. There had been precedent for this, as ''[[Anomalocaris]]'' had been originally identified as three separate creatures before being identified as a single huge (for its time) {{convert|1.12|ft|cm|1|abbr=~|adj=mid||order=flip}} to {{convert|1.24|ft|cm|1|adj=mid|-long|order=flip}} creature.<ref name="Gould"/>

In 1991, Lars Ramskold and [[Hou Xianguang]], working with additional specimens of a "hallucigenid", ''[[Microdictyon]]'', from the lower [[Cambrian]] [[Maotianshan shales]] of China, reinterpreted ''Hallucigenia'' as a [[lobopodian]], a legged worm-like taxon which were still thought to be exclusively related to [[onychophoran]] (velvet worm), carnivorous animals that resemble a caterpillar and shoot a sticky substance from their papillae to ensnare their prey,<ref>{{Cite journal |last=Gould |first=Stephen, Jay |date=1992 |title=The Reversal of Hallucigenia. |url= |journal=Natural History |volume=101 |issue=1 |pages=12 |via=}}</ref> at that time.<ref name="Ramsköld-1991" /><ref name="Ortega-Hernández-2015" /> They inverted it, interpreting the tentacles, which they believe to be paired, as walking structures and the spines as protective.<ref name="Ramsköld-1991" /> Further preparation of fossil specimens showed that "second legs" were buried at an angle to the plane along which the rock had split, and could be revealed by removing the overlying sediment.<ref name="Ramsköld-1992">{{cite journal |first1=Lars |last1=Ramsköld |date=April 1992 |title=The second leg row of Hallucigenia discovered |journal=Lethaia |volume=25 |issue=2 |pages=221–4 |doi=10.1111/j.1502-3931.1992.tb01389.x}}</ref> Ramskold and Hou also believe that the blob-like "head" is actually a stain that appears in many specimens, not a preserved portion of the anatomy.<ref name="Ramsköld-1991">{{cite journal |last1=Ramsköld |first1=L. |last2=Hou |first2=X.-G. |title=New early Cambrian animal and onychophoran affinities of enigmatic metazoans |journal=Nature |volume=351 |pages=225–8 |year=1991 |bibcode=1991Natur.351..225R |doi=10.1038/351225a0 |issue=6323 |s2cid=4309565 }}</ref> This stain may be an artifact of decomposition.<ref name="Smith-2015" />