Hallucishaniids
{{Short description|Possibly extinct group of lobopodians}}
{{Automatic taxobox
| fossil_range = {{fossil range|Cambrian Stage 3|Moscovian|latest=Recent}} Possibly ancestors of tardigrades.
| image = 20210000 Luolishaniids Luolishaniidae Luolishaniida.png
| image_caption = Diagrammatic reconstructions of various luolishaniids
| display_parents = 2
| taxon = Hallucishaniids
| authority = Smith & Caron, 2015
| type_species =
| type_species_authority =
| subdivision_ranks = Families
| subdivision = *†Hallucigeniidae
}}
"Hallucishaniids" are a clade of lobopodians uniting the families Hallucigeniidae and Luolishaniidae.{{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=July 2015 |volume=523 |issue=7558 |pages=75–78 |doi=10.1038/nature14573|pmid=26106857 |bibcode=2015Natur.523...75S |url=https://durham-repository.worktribe.com/output/1430240 }} The name of this clade is a portmanteau of its two constituent families.
Morphology and description
File:20210000 Hallucigenia diagrammatic reconstruction.png species]]
Hallucishaniids have two or three body zones. The first of these contains the eyespot-bearing head and several pairs of feathery appendages likely specialised for filter feeding. The second, larger zone consists of many pairs of clawed limbs used for walking with each pair corresponding to a sclerite, with a third zone present in Ovatiovermis where the feathery appendages continue with far shorter branches, and clawed limbs are reduced to the last few pairs.{{cite journal |last1=Caron |first1=Jean-Bernard |last2=Aria |first2=Cédric |title=Cambrian suspension-feeding lobopodians and the early radiation of panarthropods |journal=BMC Evolutionary Biology |date=December 2017 |volume=17 |issue=1 |page=29 |doi=10.1186/s12862-016-0858-y|doi-access=free |pmid=28137244 |pmc=5282736 |bibcode=2017BMCEE..17...29C |hdl=1807/83344 |hdl-access=free }} The limb claws seem to alternate which direction they face. Most hallucishaniids have spine-like sclerites which vary in width and length, however some like Cardiodictyon have more plate-like sclerites,{{cite journal |last1=Strausfeld |first1=Nicholas J. |last2=Hou |first2=Xianguang |last3=Sayre |first3=Marcel E. |last4=Hirth |first4=Frank |title=The lower Cambrian lobopodian Cardiodictyon resolves the origin of euarthropod brains |journal=Science |date=25 November 2022 |volume=378 |issue=6622 |pages=905–909 |doi=10.1126/science.abn6264|pmid=36423269 |bibcode=2022Sci...378..905S }} and Ovatiovermis as well as Facivermis lack them entirely. Thanahita is especially bizarre, as while it retains sclerites they are rather randomly distributed along the body and have several tufts near their tips which make them vaguely resemble coral polyps.{{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 |title=A three-dimensionally preserved lobopodian from the Herefordshire (Silurian) Lagerstätte, UK |journal=Royal Society Open Science |date=August 2018 |volume=5 |issue=8 |pages=172101 |doi=10.1098/rsos.172101|pmid=30224988 |pmc=6124121 }} The sclerites are paired in hallucigeniids, but luolishaniids have three or more per lobopod pair; some, such as Acinocricus and Collinsium, have rings of sclerites in between their lobopods.{{cite journal |last1=Yang |first1=Jie |last2=Ortega-Hernández |first2=Javier |last3=Gerber |first3=Sylvain |last4=Butterfield |first4=Nicholas J. |last5=Hou |first5=Jin-bo |last6=Lan |first6=Tian |last7=Zhang |first7=Xi-guang |title=A superarmored lobopodian from the Cambrian of China and early disparity in the evolution of Onychophora |journal=Proceedings of the National Academy of Sciences |date=14 July 2015 |volume=112 |issue=28 |pages=8678–8683 |doi=10.1073/pnas.1505596112|doi-access=free |pmid=26124122 |bibcode=2015PNAS..112.8678Y |pmc=4507230 }} In addition, luolishaniids often have a circular, flat head sclerite.
Hallucishaniids have just one or two claws per limb, as opposed to the three or more of other lobopodians like Aysheaia. Luolishaniids in particular also have hardened sheets within their bodies, likely to support the larger, broader spines they often bear. This feature is particularly prominent in Entothyreos, which has large shield-like sheets alongside a partly arthrodised last pair of limbs.{{cite journal |last1=Aria |first1=Cédric |last2=Caron |first2=Jean-Bernard |title=Deep origin of articulation strategies in panarthropods: evidence from a new luolishaniid lobopodian (Panarthropoda) from the Tulip Beds, Burgess Shale |journal=Journal of Systematic Palaeontology |date=31 December 2024 |volume=22 |issue=1 |doi=10.1080/14772019.2024.2356090|bibcode=2024JSPal..2256090A }} Arguably the most derived hallucishaniid of all is Facivermis, which entirely lacks limbs except for its filtering appendages, with a pear-shaped posterior body end, alongside seemingly living in tubes much like some modern polychaetes.{{cite journal |last1=Howard |first1=Richard J. |last2=Hou |first2=Xianguang |last3=Edgecombe |first3=Gregory D. |last4=Salge |first4=Tobias |last5=Shi |first5=Xiaomei |last6=Ma |first6=Xiaoya |title=A Tube-Dwelling Early Cambrian Lobopodian |journal=Current Biology |date=April 2020 |volume=30 |issue=8 |pages=1529–1536.e2 |doi=10.1016/j.cub.2020.01.075|pmid=32109391 |bibcode=2020CBio...30E1529H |doi-access=free |hdl=10141/623115 |hdl-access=free }}
Hallucishaniids are among the longest-lasting lobopodians, with fossils extending from the Cambrian to the Carboniferous.{{cite journal |last1=Haug |first1=Joachim T. |last2=Mayer |first2=Georg |last3=Haug |first3=Carolin |last4=Briggs |first4=Derek E.G. |title=A Carboniferous Non-Onychophoran Lobopodian Reveals Long-Term Survival of a Cambrian Morphotype |journal=Current Biology |date=September 2012 |volume=22 |issue=18 |pages=1673–1675 |doi=10.1016/j.cub.2012.06.066|pmid=22885062 |bibcode=2012CBio...22.1673H }} The luolishaniids (and specifically Ovatiovermis) are also likely ancestral to tardigrades.{{cite journal |last1=Kihm |first1=Ji-Hoon |last2=Smith |first2=Frank W. |last3=Kim |first3=Sanghee |last4=Rho |first4=Hyun Soo |last5=Zhang |first5=Xingliang |last6=Liu |first6=Jianni |last7=Park |first7=Tae-Yoon S. |title=Cambrian lobopodians shed light on the origin of the tardigrade body plan |journal=Proceedings of the National Academy of Sciences |date=11 July 2023 |volume=120 |issue=28 |pages=e2211251120 |doi=10.1073/pnas.2211251120|doi-access=free |pmid=37399417 |pmc=10334802 |bibcode=2023PNAS..12011251K }}