Palaeoscolecid#Wronascolex

Palaeoscolecids bear an annulated trunk ornamented with circular patterns of phosphatic tesselating plates; a layered cuticle; and an armoured proboscis. They are long and narrow, and can reach tens of centimetres in length. Their cuticle is annulated, typically in complete rings, but sometimes the rings split or only encircle part of the trunk. Each annulus is essentially identical to its neighbours; the only trunk differentiation is at the anterior and posterior. The anterior is radially symmetrical, typically comprising an introvert, whereas the trunk is bilaterally symmetrical. The posterior hosts the terminal anus and sometimes one or two hooks. 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.

Palaeoscolecids can grow by the continuous addition of plates, or by the continued growth of individual plates.{{Cite journal | doi = 10.1016/j.palwor.2023.03.005| title = Growth patterns of palaeoscolecid sclerites from the Furongian (Upper Cambrian) Wangcun section, western Hunan, South China| date = 2023| last1 = Xian| first1 = Xiao-Feng| last2 = Eriksson| first2 = Mats E.| last3 = Zhang| first3 = Hua-Qiao| journal = Palaeoworld| s2cid = 257601719}}

Palaeoscolecids are somewhat challenging to define, and probably represent a paraphyletic grouping. Their most current systematic diagnosis{{cite journal|doi=10.1111/pala.12210|title=A palaeoscolecid worm from the Burgess Shale|journal=Palaeontology|volume=58|issue=6|pages=973–979|year=2015|last1=Smith|first1=Martin R.|s2cid=86747103 |doi-access=free|bibcode=2015Palgy..58..973S }} references their annulated worm-like body form, the presence of rows (usually) of phosphatic plates, and a straight gut, with the anus at the end of the animal. The group contains a wide and continuous spectrum of morphological variety, making further division of the group difficult; moreover, non-palaeoscolecid taxa likely evolved from palaeoscolecid-like ancestors, and it is thus difficult to demarcate a single clade that corresponds to the palaeoscolecid concept.

They are considered by some to belong to the Cycloneuralia,{{cite journal| last1 = Conway Morris | first1 = S.| last2 = Peel | first2 = J. S. | year = 2010 | title = New palaeoscolecidan worms from the Lower Cambrian: Sirius Passet, Latham Shale, and Kinzers Shale | journal = Acta Palaeontologica Polonica | volume = 55 | issue = 1 | pages = 141–156 | url = http://app.pan.pl/article/item/app20090058.html| doi = 10.4202/app.2009.0058| citeseerx = 10.1.1.620.4930 | s2cid = 54037571}} although their position within this group is unresolved; they may lie with the priapulids or Nematomorpha.conference, http://gf.tmsoc.org/Documents/Mikro2009/GFSP15.pdf#page=82

They have also been described as a sister-group to the Ecdysozoa,{{cite journal| last1 = Peel | first1 = J. S.| title = A Corset-Like Fossil from the Cambrian Sirius Passet Lagerstätte of North Greenland and Its Implications for Cycloneuralian Evolution| journal = Journal of Paleontology| volume = 84| issue = 2| pages = 332–340| date = March 2010| doi = 10.1666/09-102R.1| bibcode = 2010JPal...84..332P| s2cid = 86256781}} although as more characters are described a position closer to the priapulids becomes most probable.{{cite journal

| last1 = Harvey | first1 = T. H.

| last2 = Dong | first2 = X.

| last3 = Donoghue | first3 = P. C.

| title = Are palaeoscolecids ancestral ecdysozoans?

| journal = Evolution & Development

| volume = 12

| issue = 2

| pages = 177–200

| year = 2010

| pmid = 20433458

| doi = 10.1111/j.1525-142X.2010.00403.x

| s2cid = 16872271

}} This said, their pharynx has the sixfold symmetry that likely characterised the ancestral ecdysozoan, rather than the fivefold symmetry of priapulans.{{Cite journal | doi = 10.1017/S0016756820000308| title = Introvert and pharynx of Mafangscolex, a Cambrian palaeoscolecid| year = 2020| last1 = Yang| first1 = Jie| last2 = Smith| first2 = Martin R.| last3 = Zhang| first3 = Xi-Guang| last4 = Yang| first4 = Xiao-yu| journal = Geological Magazine| volume = 157| issue = 12| pages = 2044–2050| bibcode = 2020GeoM..157.2044Y| s2cid = 219092881| url = http://dro.dur.ac.uk/30652/1/30652.pdf}} A nematomorph affinity appears to be an artefact that results from under-sampling of the priapulid stem group. Their relationship with Archaeopriapulida is unclear, and either group may be paraphyletic to the other. Some authors choose to include paleoscolecids within Priapulida.{{Cite journal |last1=Whitaker |first1=Anna F. |last2=Jamison |first2=Paul G. |last3=Schiffbauer |first3=James D. |last4=Kimmig |first4=Julien |date=December 2020 |title=Re-description of the Spence Shale palaeoscolecids in light of new morphological features with comments on palaeoscolecid taxonomy and taphonomy |url=http://link.springer.com/10.1007/s12542-020-00516-9 |journal=PalZ |language=en |volume=94 |issue=4 |pages=661–674 |doi=10.1007/s12542-020-00516-9 |bibcode=2020PalZ...94..661W |s2cid=211479504 |issn=0031-0220}}

Martin R. Smith and Alavya Dhungana suggested in a 2022 publication that palaeoscolecids are a grade including sister taxa to Panarthropoda, highlighting similarities between the dorsal plates of taxa such as cricocosmiids and those of lobopodians such as Microdictyon.{{Cite journal | doi = 10.1144/jgs2021-111| title = Discussion on 'Tabelliscolex (Cricocosmiidae: Palaeoscolecidomorpha) from the early Cambrian Chengjiang Biota and the evolution of seriation in Ecdysozoa' by Shi et al. 2021 (JGS, jgs2021-060)| year = 2022| last1 = Smith| first1 = Martin Ross| last2 = Dhungana| first2 = Alavya| journal = Journal of the Geological Society| volume = 179| issue = 3| bibcode = 2022JGSoc.179..111S| s2cid = 244850491| doi-access = free}} This proposal was made in response to a 2021 paper that found in a phylogenetic analysis that paleoscolecids were stem-group priapulids.{{Cite journal |last1=Shi |first1=Xiaomei |last2=Howard |first2=Richard J. |last3=Edgecombe |first3=Gregory D. |last4=Hou |first4=Xianguang |last5=Ma |first5=Xiaoya |date=March 2022 |title=Tabelliscolex (Cricocosmiidae: Palaeoscolecidomorpha) from the early Cambrian Chengjiang Biota and the evolution of seriation in Ecdysozoa |journal=Journal of the Geological Society |language=en |volume=179 |issue=2 |pages=jgs2021–060 |doi=10.1144/jgs2021-060 |issn=0016-7649|doi-access=free |bibcode=2022JGSoc.179...60S }}

As palaeoscolecids may represent a grade rather than a clade, drawing up a formal taxonomy proves problematic. What is more, two parallel taxonomies exist: a form taxonomy for sclerites, and a true taxonomy for articulated fossils.

The most recent holistic study of priapulids by Harvey et al. (2010) defines a core of palaeoscolecids characterized by a cuticle that is made up of interlocking plates of multiple sizes, and a looser assemblage (palaeoscolecids sensu lato) including other unconfirmed and palaeoscolecid-like forms:

• Palaeoscolex piscatorum (early Ordovician)
• Palaeoscolex (=Mafangscolex) sinensis'' (early Cambrian, China)
• Sanxiascolex papillogyrus (early Cambrian, China){{cite journal|doi=10.1111/1755-6724.12724|title=Distinctive Scleritome with Marginal Tubercles of a New Palaeoscolecid Worm from the Shipai Fauna (Cambrian Epoch 2) at Three Gorges, South China|journal=Acta Geologica Sinica - English Edition|volume=90|issue=3|pages=807|year=2016|last1=Yuning|first1=Yang|last2=Xingliang|first2=Zhang|bibcode=2016AcGlS..90..807Y |s2cid=132852259 }}
• Scathascolex minor (Burgess Shale, mid-Cambrian)
• Arrakiscolex aasei (Drumian, Cambrian; Marjum Formation, Utah){{Cite journal | doi = 10.4202/app.00875.2021| title = First palaeoscolecid from the Cambrian (Miaolingian, Drumian) Marjum Formation of western Utah| year = 2021| last1 = Leibach| first1 = Wade| last2 = Lerosey-Aubril| first2 = Rudy| last3 = Whitaker| first3 = Anna| last4 = Schiffbauer| first4 = James| last5 = Kimmig| first5 = Julien| journal = Acta Palaeontologica Polonica| volume = 66| s2cid = 239731912| doi-access = free}}
• Sahascolex (early Cambrian of Siberia)
• Gamascolex (early Ordovician, Czech Rep.)
• Plasmuscolex (early Ordovician, Czech Rep.)
• ?Guanduscolex minor (early Cambrian, China)
• ? Family Chalazoscolecidae:
• ?Chalazoscolex (Sirius Passet; fine structure unclear)
• ?Xystoscolex (Sirius Passet; fine structure unclear)
• Wronascolex? johanssoni (mid-Cambrian, Scandinavia){{cite journal|doi=10.1002/spp2.1067|title=Cambrian palaeoscolecids (Cycloneuralia) of southern Scandinavia|journal=Papers in Palaeontology|volume=3|pages=21–48|year=2016|last1=Streng|first1=Michael|last2=Ebbestad|first2=Jan Ove R.|last3=Berg-Madsen|first3=Vivianne|s2cid=89406537 }}
• Maotianshania? sp. (late early Cambrian, Scandinavia)
• Radnorscolex (2 species, Ordovician-Silurian, Great Britain)

(from Orsten-type deposits, preserved in three dimensions)

• Austroscolex Muller & Hinz 1993{{cite journal | last1 = Müller | first1 = K. J. | last2 = Hinz-Schallreuter | first2 = I. | year = 1993 | title = Palaeoscolecid worms from the Middle Cambrian of Australia | url = http://www.palass-pubs.org/palaeontology/pdf/Vol36/Pages | journal = Palaeontology | volume = 36 | pages = 549–592 }}
• Corallioscolex Muller & Hinz 1993
• Euryscolex Muller & Hinz 1993*
• Hadimopanella Gedik 1977{{cite journal | doi = 10.1017/S0016756809990082| title = Palaeoscolecid scleritome fragments with Hadimopanella plates from the early Cambrian of South Australia| journal = Geological Magazine| volume = 147| pages = 86–97| year = 2009| last1 = Topper | first1 = T. P. | last2 = Brock | first2 = G. A. | last3 = Skovsted | first3 = C. B. | last4 = Paterson | first4 = J. R. | s2cid = 54916222}}
• Kaloskolex Muller & Hinz 1993
• Milaculum Muller 1973
• Murrayscolex Muller & Hinz 1993
• Pantoioscolex Muller & Hinz 1993
• Rhomboscolex Muller & Hinz 1993
• Schistoscolex Muller & Hinz 1993
• Shergoldiscolex Muller & Hinz 1993
• Thoracoscolex Muller & Hinz 1993

• Dispinoscolex {{Cite journal | doi = 10.1016/j.palwor.2023.03.005| title = Growth patterns of palaeoscolecid sclerites from the Furongian (Upper Cambrian) Wangcun section, western Hunan, South China| date = 2023| last1 = Xian| first1 = Xiao-Feng| last2 = Eriksson| first2 = Mats E.| last3 = Zhang| first3 = Hua-Qiao| journal = Palaeoworld| s2cid = 257601719}}
• Houscolex Zhang & Pratt{{cite journal | last1 = Zhang | first1 = X.-G. | last2 = Pratt | first2 = B. R. | year = 1996 | title = Early Cambrian palaeoscolecid cuticles from Skaanxi, China | journal = Journal of Paleontology | volume = 70 | issue = 2 | pages = 275–279 | doi = 10.1017/s0022336000023350 | bibcode = 1996JPal...70..275Z | s2cid = 132183034 }} (Order and Family uncertain)
• Hunanoscolex Duan & DongDuan B, Dong X. 2013. Furongian (Late Cambrian) palaeoscolecid cuticles from Hunan Province, South China: the growth impact on the worm cuticle. Acta Scientiarum Naturalium Universitatis Pekinensis 49: 591–602. https://www.researchgate.net/profile/Xi_Ping_Dong/publication/264275844_Furongian_%28_Late_Cambrian_%29_Palaeoscolecid_Cuticles_from_Hunan_Province__South_China_the_Growth_Impact_on_Worm_Cuticle/links/53d894d70cf2631430c3250c.pdf (= Ornatoscolex Duan & Dong){{Cite journal | doi = 10.1016/j.palwor.2023.03.005| title = Growth patterns of palaeoscolecid sclerites from the Furongian (Upper Cambrian) Wangcun section, western Hunan, South China| date = 2023| last1 = Xian| first1 = Xiao-Feng| last2 = Eriksson| first2 = Mats E.| last3 = Zhang| first3 = Hua-Qiao| journal = Palaeoworld| s2cid = 257601719}}

Other long and narrow Palaeozoic worms that exhibit an invariant body width are commonly referred to the palaeoscolecids, even though they lack the cuticular structure that defines the group; this 'Palaeoscolecid sensu lato' group includes Louisella, Cricocosmia, Tabelliscolex, Tylotites and others.

Maotianshania and, by extension, the family Maotianshaniidae, was excluded from the "Palaeoscolecids sensu stricto" by Harvey et al. (2010), but it has been argued that members of this family do exhibit the requisite cuticular structure, if discreetly.

It is possible that Markuelia represents an embryonic Palaeoscolecid.{{cite journal | last1 = Duan | first1 = B. | last2 = Dong | first2 = X. -P. | last3 = Donoghue | first3 = P. C. J. | doi = 10.1111/j.1475-4983.2012.01148.x | title = New palaeoscolecid worms from the Furongian (upper Cambrian) of Hunan, South China: Is Markuelia an embryonic palaeoscolecid? | journal = Palaeontology | volume = 55 | issue = 3 | pages = 613–622 | year = 2012 | bibcode = 2012Palgy..55..613D | s2cid = 53485143 | url = https://www.dora.lib4ri.ch/psi/islandora/object/psi%3A11695 }}

; Order Uncertain

• Family Chalazoscolecidae Conway Morris & Peel 2010
• : Defined by the presence of smooth, folded and sclerite-bearing cuticular regions
• Chalazoscolex pharkus
• Xystoscolex boreogyrus

; Order Cricocosmida Han et al. 2007{{cite journal |url=https://www.app.pan.pl/archive/published/app52/app52-423.pdf|author=Han, J., Liu, J., Zhang, Z., Zhang, X., and Shu, D.|year= 2007|title= Trunk ornament on the palaeoscolecid worms Cricocosmia and Tabelliscolex from the Early Cambrian Chengjiang deposits of China|journal= Acta Palaeontologica Polonica |volume=52|number=2|pages=423–431}}

: Defined by the presence of an unarmoured neck between the proboscis and the trunk, and a single pair of posterior hooks.

:* Family Cricocosmiidae

:** Tabelliscolex:

:*** Tabelliscolex hexagonus

:*** Tabelliscolex maanshanensis

:*** Tabelliscolex chengjiangensis

:** Cricocosmia:

:*** Cricocosmia jinningensis

:** Houscolex

:* Family Maotianshaniidae

:** Maotianshania cylindrica Sun and Huo, 1987

:* Family Palaeoscolecidae

:**Wronascolex

:**:Defined by presence of Hadimopanella sclerites with three to ten nodes.{{cite journal | last1 = García-Bellido | first1 = D. C. | last2 = Paterson | first2 = J. R. | last3 = Edgecombe | first3 = G. D. | doi = 10.1016/j.gr.2012.12.002 | title = Cambrian palaeoscolecids (Cycloneuralia) from Gondwana and reappraisal of species assigned to Palaeoscolex | journal = Gondwana Research | volume = 24 | issue = 2 | pages = 780–795 | year = 2013 | bibcode = 2013GondR..24..780G }}

:**Palaeoscolex

:**:Defined by presence of Milaculum-type plates, i.e. rectangular with parallel rows of nodes

:**Utahscolex Whitaker et al. 2020{{cite journal | last1 = Whitaker | first1 = Anna F. | last2 = Jamison | first2 = Paul G. | last3 = Schiffbauer | first3 = James D. | last4 = Kimmig | first4 = Julien K. | year = 2020 | title = Re‑description of the Spence Shale palaeoscolecids in light of new morphological features with comments on palaeoscolecid taxonomy and taphonomy | journal = PalZ | volume = 94 | issue = 4 | pages = 661–674 | doi = 10.1007/s12542-020-00516-9 | bibcode = 2020PalZ...94..661W | s2cid = 211479504 }}

:** Ashetscolex Muir et al 2014{{cite journal|doi=10.1016/j.palwor.2013.06.003|title=Palaeoscolecidan worms and a possible nematode from the Early Ordovician of South China|journal=Palaeoworld|volume=23|pages=15–24|year=2014|last1=Muir|first1=Lucy A.|last2=Ng|first2=Tin-Wai|last3=Li|first3=Xiang-Feng|last4=Zhang|first4=Yuan-Dong|last5=Lin|first5=Jih-Pai}}

:** Sanduscolex Muir et al 2014

:* Family Tylotitidae

:** Tylotites petiolaris Luo and Hu, 1999

; Other Palaeoscolecidae or unassigned

{{linked species list

|Gamascolex|Kraft & Mergl, 1989

|Guanduscolex minor|Hu et al., 2008

|Louisella pedunculata|

|Palaeoscolex sinensis|Hou & Sun 1988 ({{=}}Mafangscolex siniensis, Parapalaeoscolex sinensis){{cite journal | doi = 10.1016/j.palaeo.2013.11.004| title = The burrow dwelling behavior and locomotion of palaeoscolecidian worms: New fossil evidence from the Cambrian Chengjiang fauna| journal = Palaeogeography, Palaeoclimatology, Palaeoecology| volume = 398| pages = 154–164| year = 2014| last1 = Huang | first1 = D. | last2 = Chen | first2 = J. | last3 = Zhu | first3 = M. | last4 = Zhao | first4 = F. | bibcode = 2014PPP...398..154H}}

|Paramaotianshania zijunia|Hu et al 2012

|Wudingscolex sapushanensis|Hu et al 2012

}}

; Microfossil material

{{linked species list

|Floraconformis | Goñi et al. 2023{{Cite journal | doi = 10.4202/app.01030.2022| title = New Palaeoscolecid plates from the Cambrian Stage 3 of northern Mongolia| year = 2023| last1 = Goñi| first1 = Iban| last2 = Skovsted| first2 = Christian| last3 = Li| first3 = Luoyang| last4 = Li| first4 = Guoxiang| last5 = Betts| first5 = Marissa| last6 = Dorjnamjaa| first6 = Dorj| last7 = Altanshagai| first7 = Gundsambuu| last8 = Enkhbaatar| first8 = Batkhuyag| last9 = Topper| first9 = Timothy| journal = Acta Palaeontologica Polonica| volume = 68| s2cid = 256711586| doi-access = free}}

|Hadimopanella |

|Kaimenella |

|Milaculum |

|Plasmuscolex|Kraft & Mergl, 1989

|Protoscolex|

|Sahascolex|Ivantsov & Wrona, 2004

|Utahphospha|{{cite journal | jstor = 1304225| volume=55| issue = 2| pages=395–400 | title = An Ordovician Occurrence of Utahphospha Müller & Miller | journal = Journal of Paleontology| last1 = Repetski| first1 = John E.| year = 1981}}

|Yunnanoscolex magnus|Hu et al 2012{{cite journal | doi = 10.3140/bull.geosci.1238| title = A new priapulid assemblage from the early Cambrian Guanshan fossil Lagerstätte of SW China| journal = Bulletin of Geosciences| pages = 93–106| year = 2012| last1 = Hu | first1 = S.| last2 = Steiner | first2 = M.| last3 = Zhu | first3 = M.| last4 = Luo | first4 = H.| last5 = Forchielli | first5 = A.| last6 = Keupp | first6 = H.| last7 = Zhao | first7 = F. | last8 = Liu | first8 = Q.| doi-access = free}}

}}

Palaeoscolex has been abused as a wastebasket taxon for palaeoscolecid macrofossils. The most recent proposal is that Palaeoscolex should only include taxa with Milaculum-type sclerites, as in the type species P. piscatorum.{{cite journal | last1 = Conway | first1 = Morris S. | year = 1997 | title = The cuticular structure of the 495-Myr-old type species of the fossil worm ~Palaeoscolex~, ~P. piscatorum~ (?Priapulida) | journal = Zoological Journal of the Linnean Society | volume = 119 | pages = 69–82 | doi = 10.1111/j.1096-3642.1997.tb00136.x | doi-access = free }} As such, P. ratcliffei and P. huainanensis should not be included in Palaeoscolex.

Originally described from Siberia, Wronascolex should now be considered to include all taxa with Hadimopanella sclerites that have 3–10 nodes in a single circle, perhaps including Yunnanoscolex.

Though these genera have sclerites that resemble Hadimopanella knappologicum, they remain valid genera.

This genus{{cite book|author=Shixue Hu|date=October 2005|url=https://www.researchgate.net/publication/258246958|title=Taphonomy and palaeoecology of the early Cambrian Chengjiang Biota from eastern Yunnan, China|publisher=Berliner Paläobiologische Abhandlungen|volume=7|pages=1–197|isbn=3980853179}} has simple sclerites with a single (small but prominent) node in the middle, so can be separated from Palaeoscolex(unless this simplicity is taphonomic). Its introvert has a six-fold symmetry, whereas its proboscis has quincuncially arranged teeth that resemble those of other Cambrian ecdysozoan worms.

Originally described from the Spence Shale of Utah, Utahscolex has four transverse rings of plates per annulus, arranged as two 'bands' of double rows of plates separated by a central naked zone. Occasionally, single row bifurcates into two rows (for up to 6 rows per annulus). The plates are circular, and unornamented. Platelets and microplates are absent.

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Category:Cambrian first appearances

Category:Silurian extinctions