Selkirkia columbia, from Smith et al. (2015).

Belongs within: Eumetazoa.
Contains: Cycloneuralia, Onychophora, Tardigrada, Arthropoda.

The Ecdysozoa is a clade of animals primarily identified by molecular analyses though members of the clade are also characterised by the possession of a thick cuticle that is periodically moulted, together with a ventral nerve cord (Cavalier-Smith 1998). Ecdysozoans include arthropods and related taxa, together with a number of worm-like groups including nematodes and priapulids. Other ecdysozoans include the Loricifera, minute animals found in marine sediment in which the body is contained within a protective shell or lorica. Ecdysozoans with functional legs form a clade Panarthropoda; in members of the Onychophora and Tardigrada, as well as various early fossil members of the clade, the legs are fleshy and un-segmented.

The fossil record includes a number of worm-like taxa from the early Palaeozoic such as Selkirkia and Palaeoscolex that are believed to represent relatives of the priapulids, many of which resembled priapulids in the possession of a more or less invertable, spinose proboscis. Members of the Middle Cambrian genus Selkirkia lived enclosed in an elongate, probably chitinous tube.

<==Ecdysozoa (see below for synonymy)
    |  i. s.: HamulariaG20
    |           |--H. cylindricaG20
    |           `--H. nodulosaR26
    |         LyorhynchusG20
    |           |--L. denticulatusG20
    |           `--L. lepidopus Risso 1826R26
    |         Ophiostoma lepturumG20
    |--+--Ancalagon [Ancalagonidae]DD04
    |  |    `--A. minor (Walcott 1911) [=Ottoia minor]SBH15
    |  `--Fieldia [Fieldiidae]DD04
    |       `--F. lanceolata Walcott 1911SHB15
    `--+--Markuelia Val’kov 1983DD04
       |    |--*M. secundaDD04
       |    `--M. hunanensis Dong, Donoghue et al. 2004DD04
          `--Panarthropoda [Tardipolypoda]SO-H14
               |--Aysheaia Walcott 1911SO-H14, CM98
               |    |--A. pedunculata Walcott 1911HM04
               |    `--A. prolata Robison 1985HM04
                       |  i. s.: Sialomorpha Poinar & Nelson 2019 [Sialomorphidae]PN19
                       |           `--*S. dominicana Poinar & Nelson 2019PN19
                       |--+--Onychodictyon ferox Hou, Ramsköld & Bergstrom 1991SO-H14, HM04
                       |  `--TardigradaSO-H14
                          |  `--+--MegadictyonSO-H14
                          |     `--JianshanopodiaSO-H14
                          `--+--Hadranax augustus Budd & Peel 1998SO-H14, HM04
                             `--+--Kerygmachela Budd 1993KBR09, W96
                                |    `--K. kierkegaardiKBR09
                                `--+--Pambdelurion whittingtoniSO-H14, KBR09
                                   `--Anomalocaridea [Anomalopoda]B95
                                        |--Cassubia Lendzion 1977 [Cassubiata]B95
                                        |    `--C. infercambriensis (Lendzion 1975)WS93
                                             `--Opabinia Walcott 1912SO-H14, B95
                                                  `--O. regalis Walcott 1912WS93

Ecdysozoa [Cephalorhyncha, Dicephalosomata, Haemopoda, Introverta, Lobopoda, Mandibulopoda, Nematoidea, Nematozoa, Opabiniida, Opabiniidacea, Podophora, Probosciferidea, Scalidophora, Scalidorhyncha, Tritocerebra, Uniantennata, Uniramia]

*Type species of generic name indicated


[B95] Bousfield, E. L. 1995. A contribution to the natural classification of Lower and Middle Cambrian arthropods: food-gathering and feeding mechanisms. Amphipacifica 2: 3–34.

[CM98] Conway Morris, S. 1998. The Crucible of Creation. Oxford University Press: Oxford.

[DD04] Dong, X-P., P. C. J. Donoghue, H. Cheng & J.-B. Liu. 2004. Fossil embryos from the Middle and Late Cambrian period of Hunan, south China. Nature 427: 237–240.

[G20] Goldfuss, G. A. 1820. Handbuch der Naturgeschichte vol. 3. Handbuch der Zoologie pt 1. Johann Leonhard Schrag: Nürnberg.

[HM04] Hou, X.-G., X.-Y. Ma, J. Zhao & J. Bergström. 2004. The lobopodian Paucipodia inermis from the Lower Cambrian Chengjiang fauna, Yunnan, China. Lethaia 37: 235–244.

[KBR09] Kühl, G., D. E. G. Briggs & J. Rust. 2009. A great-appendage arthropod with a radial mouth from the Lower Devonian Hunsrück Slate, Germany. Science 323: 771–773.

[OH17] Ou, Q., J. Han, Z. Zhang, D. Shu, G. Sun & G. Mayer. 2017. Three Cambrian fossils assembled into an extinct body plan of cnidarian affinity. Proceedings of the National Academy of Sciences of the USA 114 (33): 8835–8840.

[PN19] Poinar, G., & D. R. Nelson. 2019. A new microinvertebrate with features of mites and tardigrades in Dominican amber. Invertebrate Biology 138 (4): e12265.

[R26] Risso, A. 1826. Histoire naturelle des principales productions de l’Europe méridionale et particulièrement de celles des environs de Nice et des Alpes maritimes vol. 5. F.-G. Levrault: Paris.

[SHB15] Smith, M. R., T. H. P. Harvey & N. J. Butterfield. 2015. The macro- and microfossil record of the Cambrian priapulid Ottoia. Palaeontology 58 (4): 705–721.

[SO-H14] Smith, M. R., & J. Ortega-Hernández. 2014. Hallucigenia‘s onychophoran-like claws and the case for Tactopoda. Nature 514: 363–366.

[VS14] Vinther, J., M. Stein, N. R. Longrich & D. A. T. Harper. 2014. A suspension-feeding anomalocarid from the Early Cambrian. Nature 507: 496–499.

[W96] Waggoner, B. M. 1996. Phylogenetic hypotheses of the relationships of arthropods to Precambrian and Cambrian problematic fossil taxa. Systematic Biology 45 (2): 190–222.

[WS93] Wills, M. A., & J. J. Sepkoski Jr. 1993. Problematica. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 543–554. Chapman & Hall: London.

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