Hallucishaniids
| Hallucishaniids Temporal range: Possibly ancestors of tardigrades.
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| Diagrammatic reconstructions of various luolishaniids | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| (unranked): | Panarthropoda |
| Phylum: | †"Lobopodia" |
| Clade: | †Hallucishaniids Smith & Caron, 2015 |
| Families | |
"Hallucishaniids" are a clade of lobopodians uniting the families Hallucigeniidae and Luolishaniidae.[1] The name of this clade is a portmanteau of its two constituent families.
Morphology and description
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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.[2] 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,[3] 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.[4] 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.[5] 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.[6] 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. In addition, it seemingly lived in tubes much like some modern polychaetes.[7]
Hallucishaniids are among the longest-lasting lobopodians, with fossils extending from the Cambrian to the Carboniferous.[8] In addition, the luolishaniids (and specifically Ovatiovermis) are likely ancestral to tardigrades.[9]
References
[edit]- ^ Smith, Martin R.; Caron, Jean-Bernard (July 2015). "Hallucigenia's head and the pharyngeal armature of early ecdysozoans". Nature. 523 (7558): 75–78. Bibcode:2015Natur.523...75S. doi:10.1038/nature14573. PMID 26106857.
- ^ Caron, Jean-Bernard; Aria, Cédric (December 2017). "Cambrian suspension-feeding lobopodians and the early radiation of panarthropods". BMC Evolutionary Biology. 17 (1): 29. Bibcode:2017BMCEE..17...29C. doi:10.1186/s12862-016-0858-y. hdl:1807/83344. PMID 28137244.
- ^ Strausfeld, Nicholas J.; Hou, Xianguang; Sayre, Marcel E.; Hirth, Frank (25 November 2022). "The lower Cambrian lobopodian Cardiodictyon resolves the origin of euarthropod brains". Science. 378 (6622): 905–909. Bibcode:2022Sci...378..905S. doi:10.1126/science.abn6264. PMID 36423269.
- ^ Siveter, Derek J.; Briggs, Derek E. G.; Siveter, David J.; Sutton, Mark D.; Legg, David (August 2018). "A three-dimensionally preserved lobopodian from the Herefordshire (Silurian) Lagerstätte, UK". Royal Society Open Science. 5 (8): 172101. doi:10.1098/rsos.172101. PMC 6124121. PMID 30224988.
- ^ Yang, Jie; Ortega-Hernández, Javier; Gerber, Sylvain; Butterfield, Nicholas J.; Hou, Jin-bo; Lan, Tian; Zhang, Xi-guang (14 July 2015). "A superarmored lobopodian from the Cambrian of China and early disparity in the evolution of Onychophora". Proceedings of the National Academy of Sciences. 112 (28): 8678–8683. Bibcode:2015PNAS..112.8678Y. doi:10.1073/pnas.1505596112. PMC 4507230. PMID 26124122.
- ^ Aria, Cédric; Caron, Jean-Bernard (31 December 2024). "Deep origin of articulation strategies in panarthropods: evidence from a new luolishaniid lobopodian (Panarthropoda) from the Tulip Beds, Burgess Shale". Journal of Systematic Palaeontology. 22 (1). Bibcode:2024JSPal..2256090A. doi:10.1080/14772019.2024.2356090.
- ^ Howard, Richard J.; Hou, Xianguang; Edgecombe, Gregory D.; Salge, Tobias; Shi, Xiaomei; Ma, Xiaoya (April 2020). "A Tube-Dwelling Early Cambrian Lobopodian". Current Biology. 30 (8): 1529–1536.e2. Bibcode:2020CBio...30E1529H. doi:10.1016/j.cub.2020.01.075. PMID 32109391.
- ^ Haug, Joachim T.; Mayer, Georg; Haug, Carolin; Briggs, Derek E.G. (September 2012). "A Carboniferous Non-Onychophoran Lobopodian Reveals Long-Term Survival of a Cambrian Morphotype". Current Biology. 22 (18): 1673–1675. Bibcode:2012CBio...22.1673H. doi:10.1016/j.cub.2012.06.066.
- ^ Kihm, Ji-Hoon; Smith, Frank W.; Kim, Sanghee; Rho, Hyun Soo; Zhang, Xingliang; Liu, Jianni; Park, Tae-Yoon S. (11 July 2023). "Cambrian lobopodians shed light on the origin of the tardigrade body plan". Proceedings of the National Academy of Sciences. 120 (28): e2211251120. Bibcode:2023PNAS..12011251K. doi:10.1073/pnas.2211251120. PMC 10334802. PMID 37399417.