Scalidophora

Scalidophora
	Ottoia prolifica from the Walcott Quarry of the Burgess Shale (Middle Cambrian) near Field, British Columbia, Canada.
Scientific classification
Kingdom:	Animalia
Subkingdom:	Eumetazoa
Clade:	ParaHoxozoa
Clade:	Bilateria
Clade:	Nephrozoa
Clade:	Protostomia
Superphylum:	Ecdysozoa
Clade:	Scalidophora; Lemburg, 1995
Phyla
Possible stem groups
	Palaeoscolecida† (possibly paraphyletic) †Chalazoscolecidae; †Cricocosmida —possible stem arthropods; Other articulated microfossils; ; †Shergoldana; †Markuelia; †Qinscolex; †Shanscolex; †Xinliscolex; †Dahescolex; †Zhongpingscolex;
Synonyms
	Cephalorhyncha, Priapozoa

Scalidophora is a group of marine pseudocoelomate ecdysozoans that was proposed on morphological grounds to unite three phyla: the Kinorhyncha, the Priapulida and the Loricifera.^[8]^[9] The three phyla have four characters in common — chitinous cuticle that is moulted, rings of scalids 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 in Priapulus and is completely absent in Halicryptus.^[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 the Panarthropoda.^[9] Both studies supported a reduced Scalidophora comprising the Kinorhyncha and Priapulida as sister phyla. Their closest relatives are the Panarthropoda, Nematoda and Nematomorpha.

The two species in the genus Markuelia, known from fossilized embryos from the middle Cambrian, are thought to be stem 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]

References

^ Harvey, T. H.; Dong, X.; Donoghue, P. C. (March–April 2010). "Are palaeoscolecids ancestral ecdysozoans?". Evolution & Development. 12 (2): 177–200. doi:10.1111/j.1525-142X.2010.00403.x. PMID 20433458. S2CID 16872271.
^ "A possible larval roundworm from the Cambrian 'Orsten' and its bearing on the phylogeny of Cycloneuralia".
^ Dong, X. -P.; Bengtson, S.; Gostling, N. J.; Cunningham, J. A.; Harvey, T. H. P.; Kouchinsky, A.; Val'Kov, A. K.; Repetski, J. E.; Stampanoni, M.; Marone, F.; Donoghue, P. C. J. (2010). "The anatomy, taphonomy, taxonomy and systematic affinity of Markuelia: Early Cambrian to Early Ordovician scalidophorans" (PDF). Palaeontology. 53 (6): 1291–1314. Bibcode:2010Palgy..53.1291D. doi:10.1111/j.1475-4983.2010.01006.x. S2CID 53483146.
^ ^a ^b Liu, 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.
^ ^a ^b Telford, M. J.; Bourlat, S. J.; Economou, A.; Papillon, D.; Rota-Stabelli, O. (27 April 2008). "The evolution of the Ecdysozoa". Philosophical Transactions of the Royal Society B. 363 (1496): 1529–1537. doi:10.1098/rstb.2007.2243. PMC 2614232. PMID 18192181.
^ ^a ^b Yamasaki, Hiroshi; Fujimoto, Shinta; Miyazaki, Katsumi (2015-06-30). "Phylogenetic position of Loricifera inferred from nearly complete 18S and 28S rRNA gene sequences". Zoological Letters. 1: 18. doi:10.1186/s40851-015-0017-0. ISSN 2056-306X. PMC 4657359. PMID 26605063.
^ Heiner, I., Kristensen, R.H. 2005. Two new species of the genus Pliciloricus (Loricifera, Pliciloricidae) from the Faroe Bank, North Atlantic. Zoologischer Anzeiger. 243: 121–138.
^ Multicellular Animals: Volume III: Order in Nature - System Made by Man, Volum 3
^ Dirnberger, J. "Explanations and Difficulties in Invertebrate Phylogeny". Invertebrate Zoology. Kennesaw State University. Retrieved 2012-08-11.
^ 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. PMID 18322464. S2CID 4397099.

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[Harvey2010-1] Harvey, T. H.; Dong, X.; Donoghue, P. C. (March–April 2010). "Are palaeoscolecids ancestral ecdysozoans?". Evolution & Development. 12 (2): 177–200. doi:10.1111/j.1525-142X.2010.00403.x. PMID 20433458. S2CID 16872271.

[2] "A possible larval roundworm from the Cambrian 'Orsten' and its bearing on the phylogeny of Cycloneuralia".

[Dong-3] Dong, X. -P.; Bengtson, S.; Gostling, N. J.; Cunningham, J. A.; Harvey, T. H. P.; Kouchinsky, A.; Val'Kov, A. K.; Repetski, J. E.; Stampanoni, M.; Marone, F.; Donoghue, P. C. J. (2010). "The anatomy, taphonomy, taxonomy and systematic affinity of Markuelia: Early Cambrian to Early Ordovician scalidophorans" (PDF). Palaeontology. 53 (6): 1291–1314. Bibcode:2010Palgy..53.1291D. doi:10.1111/j.1475-4983.2010.01006.x. S2CID 53483146.

[qinscolex-4] Liu, 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.

[5] 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.

[6] 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.

[7] 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.

[Telford-2008-8] Telford, M. J.; Bourlat, S. J.; Economou, A.; Papillon, D.; Rota-Stabelli, O. (27 April 2008). "The evolution of the Ecdysozoa". Philosophical Transactions of the Royal Society B. 363 (1496): 1529–1537. doi:10.1098/rstb.2007.2243. PMC 2614232. PMID 18192181.

[Yamasaki-2015-9] Yamasaki, Hiroshi; Fujimoto, Shinta; Miyazaki, Katsumi (2015-06-30). "Phylogenetic position of Loricifera inferred from nearly complete 18S and 28S rRNA gene sequences". Zoological Letters. 1: 18. doi:10.1186/s40851-015-0017-0. ISSN 2056-306X. PMC 4657359. PMID 26605063.

[Heiner-10] Heiner, I., Kristensen, R.H. 2005. Two new species of the genus Pliciloricus (Loricifera, Pliciloricidae) from the Faroe Bank, North Atlantic. Zoologischer Anzeiger. 243: 121–138.

[11] Multicellular Animals: Volume III: Order in Nature - System Made by Man, Volum 3

[urlExplanations.html-12] Dirnberger, J. "Explanations and Difficulties in Invertebrate Phylogeny". Invertebrate Zoology. Kennesaw State University. Retrieved 2012-08-11.

[13] 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. PMID 18322464. S2CID 4397099.

[8]