Palaeoscolecid

Palaeoscolecid Temporal range: Upper Early Cambrian–Silurian[1] PreЄ Є O S D C P T J K Pg N
Scientific classification
Kingdom:	Animalia
clade:	Cycloneuralia
Class:	†Palaeoscolecida Conway Morris & Robinson, 1986
Families and genera (sensu Harvey et al. 2010[2])
Chalazoscolecidae Conway Morris & Peel 2010 Palaeoscolex Sahascolex Ivantsov & Wrona, 2004 Gamascolex Kraft & Mergl, 1989 Protoscolex Plasmuscolex Kraft & Mergl, 1989 Guanduscolex Hu et al., 2008 and microfossil material such as Hadimopanella Milaculum Kaimenella

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 lagerstatten.^[5] They take their name from the typifying genus Palaeoscolex.^[4]

Morphology

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

They are considered to be a clade within 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]

Taxonomy

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]

References

1. ^ ^{a b} Wills, M. A. (1 April 1998). "Cambrian and Recent Disparity: the Picture from Priapulids". Paleobiology 24 (2): 155–286. JSTOR 2401237.  edit
2. ^ ^{a b c d e f g} Harvey, T.; Dong, X.; Donoghue, P. (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. http://www.geo.uw.edu.pl/agp/table/pdf/54-1/wrona.pdf. 
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 9781405106733. http://books.google.com/?id=QOIFgqC4X_sC&pg=PA60&lpg=PA60&dq=palaeoscolecid. 
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. http://app.pan.pl/article/item/app20090058.html.  edit
7. ^ . http://www.ucl.ac.uk/EarthSci/Grzybowski/publications/GFSP15.pdf#page=82. 
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. http://www.app.pan.pl/archive/published/app52/app52-423.pdf.