Scalidophora is a group of marinepseudocoelomateecdysozoans that was proposed on morphological grounds to unite threephyla: theKinorhyncha, thePriapulida and theLoricifera.[8][9] The three phyla have four characters in common — chitinous cuticle that is moulted, rings ofscalids on the introvert, flosculi, and two rings of introvert retracts.[10] The introvert and abdomen are separated by a distinct neck region in all groups, but in adult macroscopic priapulids it becomes rudimentary inPriapulus and is completely absent inHalicryptus.[11] However, the monophyly of the Scalidophora was not supported by two molecular studies, where the position of the Loricifera was uncertain[8] or as sister to thePanarthropoda.[9] Both studies supported a reduced Scalidophora comprising the Kinorhyncha and Priapulida as sister phyla. Their closest relatives are thePanarthropoda,Nematoda andNematomorpha.
The two species in the genusMarkuelia, known from fossilized embryos from the middleCambrian, are thought to bestem scalidophorans.
The group has also been considered a single group,Cephalorhyncha,[12] with three classes.
The group is named after the spines (scalids) covering the introvert (head that can be retracted into the trunk).[13]
^abLiu, Yunhuan; Qin, Jiachen; Wang, Qi; Maas, Andreas; Duan, Baichuan; Zhang, Yanan; Zhang, Hu; Shao, Tiequan; Zhang, Huaqiao (May 2019). "New armoured scalidophorans (Ecdysozoa, Cycloneuralia) from the Cambrian Fortunian Zhangjiagou Lagerstätte, South China".Papers in Palaeontology.5 (2):241–260.Bibcode:2019PPal....5..241L.doi:10.1002/spp2.1239.
^Zhang, Hua-Qiao (September 2022). "The evolutionary relationships of the earliest known cycloneuralians and a new record from the Cambrian Fortunian of South China".Palaeoworld.31 (3):389–401.doi:10.1016/j.palwor.2021.09.003.
^Shao, T.Q.; Qin, J.C.; Shao, Y.; Liu, Y.H.; Waloszek, D.; Maas, A.; Duan, B.C.; Wang, Q.; Xu, Y.; Zhang, H.Q. (October 2020). "New macrobenthic cycloneuralians from the Fortunian (lowermost Cambrian) of South China".Precambrian Research.349 105413.Bibcode:2020PreR..34905413S.doi:10.1016/j.precamres.2019.105413.
^Shao, T.Q.; Wang, Q.; Liu, Y.H.; Qin, J.C.; Zhang, Y.N.; Liu, M.J.; Shao, Y.; Zhao, J.Y.; Zhang, H.Q. (October 2020). "A new scalidophoran animal from the Cambrian Fortunian Stage of South China and its implications for the origin and early evolution of Kinorhyncha".Precambrian Research.349 105616.Bibcode:2020PreR..34905616S.doi:10.1016/j.precamres.2020.105616.
^Heiner, I., Kristensen, R.H. 2005. Two new species of the genusPliciloricus (Loricifera, Pliciloricidae) from the Faroe Bank, North Atlantic. Zoologischer Anzeiger. 243: 121–138.
^Dunn, C. W.; Hejnol, A.; Matus, D. Q.; Pang, K.; Browne, W. E.; Smith, S. A.; Seaver, E.; Rouse, G. W.; Obst, M.; et al. (10 April 2008). "Broad Phylogenomic Sampling Improves Resolution of the Animal Tree of Life".Nature.452 (7188):745–749.Bibcode:2008Natur.452..745D.doi:10.1038/nature06614.PMID18322464.S2CID4397099.
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