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Temporal range: Upper Early Cambrian–Silurian[1]
Scientific classification e
Kingdom: Animalia
Clade: Cycloneuralia
Class: Palaeoscolecida
Conway Morris & Robinson, 1986
Families and genera
(sensu Harvey et al. 2010[2])

The palaeoscolecids are a group of ecdysozoan worms resembling armoured priapulids. They are known from the Lower Cambrian[3] to the late Silurian;[4] they are mainly found as disarticulated sclerites, but are also preserved in many of the Cambrian lagerstätten.[5] They take their name from the typifying genus Palaeoscolex.[4]


Palaeoscolecids bear an annulated trunk ornamented with circular patterns of phosphatic tesselating plates; a layered cuticle; and an armoured proboscis.[2] They are usually a few centimetres in length. There is no one character that unites the palaeoscolecids as a clade (indeed they are likely paraphyletic), and few individual specimens contain all characteristic palaeosolecid traits.[2]

Taxonomic position[edit]

They are considered to belong to the cycloneuralia,[6] although their position within this group is unresolved; they may lie with the priapulids or nematomorpha.[7] They have also been described as a sister-group to the ecdysozoa,[8] although as more characters are described a position closer to the priapulids becomes most probable.[2] A nematomorph affinity appears to be an artefact that results from under-sampling of the priapulid stem group.[2]

Other genera include Cricocosmia from the Lower Cambrian Chengjiang biota.[9] Their relationship with the archaeopriapulida is also unclear; it could be that both groups are a paraphyletic assemblage containing the priapulids.[1]


In addition to the genera listed in the taxobox, other worms are commonly referred to the palaeoscolecids, even though they lack the cuticular structure that defines the group.[2] These include Louisella, Maotianshania, Cricocosmia, Tabelliscolex, Tylotites and others.[2] It's also possible that Markuelia represents an embryonic Palaeoscolecid.[10]


  1. ^ a b Wills, M. A. (1 April 1998). "Cambrian and Recent Disparity: the Picture from Priapulids". Paleobiology 24 (2): 155–286. doi:10.2307/2401237 (inactive 2014-06-06). JSTOR 2401237.  edit
  2. ^ a b c d e f g Harvey, T. H.; Dong, X.; Donoghue, P. C. (2010). "Are palaeoscolecids ancestral ecdysozoans?". Evolution & Development 12 (2): 177–200. doi:10.1111/j.1525-142X.2010.00403.x. PMID 20433458.  edit
  3. ^ Andrey Y. Ivantsov & Ryszard Wrona (2004). "Articulated palaeoscolecid sclerite arrays from the Lower Cambrian of eastern Siberia" (PDF). Acta Geologica Polonica 54 (1): 1–22. 
  4. ^ a b Xianguang Hou, Richard Aldridge, Jan Bergström, David Siveter, Derek Siveter (2004). The Cambrian fossils of Chengjiang, China: the flowering of early animal life. Wiley-Blackwell. p. 233. ISBN 978-1-4051-0673-3. 
  5. ^ Zhu, M.; Babcock, L.; Steiner, M. (2005). "Fossilization modes in the Chengjiang Lagerstätte (Cambrian of China): testing the roles of organic preservation and diagenetic alteration in exceptional preservation". Palaeogeography Palaeoclimatology Palaeoecology 220: 31–37. doi:10.1016/j.palaeo.2003.03.001.  edit
  6. ^ Conway Morris, S.; Peel, J. S. (2010). "New palaeoscolecidan worms from the Lower Cambrian: Sirius Passet, Latham Shale, and Kinzers Shale". Acta Palaeontologica Polonica 55 (1): 141–156. doi:10.4202/app.2009.0058.  edit
  7. ^  Missing or empty |title= (help)
  8. ^ Peel, J. S. (2010). "A Corset-Like Fossil from the Cambrian Sirius Passet Lagerstätte of North Greenland and Its Implications for Cycloneuralian Evolution". Journal of Paleontology 84 (2): 332–340. doi:10.1666/09-102R.1.  edit
  9. ^ Jian Han, Jianni Liu, Zhifei Zhang, Xinglian Zhang & Degan Shu (2007). "Trunk ornament on the palaeoscolecid worms Cricocosmia and Tabelliscolex from the Early Cambrian Chengjiang deposits of China". Acta Palaeontologica Polonica 52 (2): 423–431. 
  10. ^ Duan, B.; Dong, X. -P.; Donoghue, P. C. J. (2012). "New palaeoscolecid worms from the Furongian (upper Cambrian) of Hunan, South China: Is Markuelia an embryonic palaeoscolecid?". Palaeontology 55 (3): 613. doi:10.1111/j.1475-4983.2012.01148.x.  edit