# Squamacula > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Squamacula > Markdown URL: https://mediated.wiki/source/Squamacula.md > Source: https://en.wikipedia.org/wiki/Squamacula > Source revision: 1333078936 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) {{Short description|Extinct genus of arthropods}} {{Automatic taxobox | fossil_range = {{fossil range|Cambrian Series 2}} | image = Squamacula clypeata reconstruction 19062025.png | image_alt = | image_caption = Reconstruction of ''Squamacula clypeata'' | taxon = Squamacula | authority = Hou and Bergström, 1997 | type_species = {{Extinct}}'''''Squamacula clypeata''''' | type_species_authority = Hou and Bergström, 1997{{Cite book|title=Arthropods of the Lower Cambrian Chengjiang fauna, southwest China|last1=Hou|first1=Xianguang|last2=Bergström|first2=Jan|year=1997|publisher=Scandinavian University Press|others=Bergström|isbn=8200376931|location=Oslo|oclc=38305908}}{{page needed|date=February 2020}} | subdivision_ranks = Species | subdivision = * {{Extinct}}''Squamacula clypeata'' Hou and Bergström, 1997 * {{Extinct}}''Squamacula buckorum'' Paterson et al. 2012 }} '''''Squamacula''''' is an extinct [artiopoda](/source/artiopoda)n [arthropod](/source/arthropod) from the [Cambrian Series 2](/source/Cambrian_Series_2). The type species ''S. clypeata'' was described in 1997 from the [Chengjiang biota](/source/Chengjiang_biota) of Yunnan, China. At the time of description there were only two known specimens of ''S. clypeata'', but now there are at least six known specimens.{{Cite book|title=The Cambrian fossils of Chengjiang, China : the flowering of early animal life|others=Hou, Xianguang.|date=8 March 2017 |isbn=9781118896310|edition= Second|location=Chichester, West Sussex|oclc=970396735}} In 2012 a second species ''S. buckorum'' was described from the [Emu Bay Shale](/source/Emu_Bay_Shale) of Australia.{{Cite journal|last1=Paterson|first1=John R.|last2=García-Bellido|first2=Diego C.|last3=Edgecombe|first3=Gregory D.|date=March 2012|title=New artiopodan arthropods from the early Cambrian Emu Bay Shale Konservat-Lagerstätte of South Australia|url=https://www.cambridge.org/core/product/identifier/S0022336000000354/type/journal_article|journal=Journal of Paleontology|language=en|volume=86|issue=2|pages=340–357|doi=10.1666/11-077.1|bibcode=2012JPal...86..340P |s2cid=87520649|issn=0022-3360|url-access=subscription}} == Etymology == The [genus](/source/genus) ''Squamacula'' is derived from the Latin word ''squama'', meaning scale, and the [diminutive suffix](/source/diminutive_suffix) -''culus'', indicating that the animal is relatively small. The [species](/source/species) ''clypeata'' is derived from the Latin word ''clypeatus'', meaning shield-shaped. It was named this in reference to its shield-like outline. == Description == ''Squamacula clypeata'' is flattened (dorsoventrally). It has 11 segments in total: the [cephalon](/source/cephalon_(arthropod_head)) (the head), nine thoracic [tergite](/source/tergite)s (each of which covers a [somite](/source/somite)), and one [pygidium](/source/pygidium).{{Cite journal|last1=Zhang|first1=Xingliang|last2=Han|first2=Jian|last3=Zhang|first3=Zhifei|last4=Liu|first4=Huqin|last5=Shu|first5=Degan|date=2004|title=Redescription of the Chengjiang arthropod Squamacula clypeata Hou and Bergström, from the Lower Cambrian, south-west China|journal=Palaeontology|volume=47|issue=3|pages=605–617|doi=10.1111/j.0031-0239.2004.00363.x|bibcode=2004Palgy..47..605Z |issn=1475-4983|doi-access=free}} It has a [doublure](/source/Trilobite), a piece of exoskeleton that covers part of the underside of the animal. Its doublure is, on average, about twice as long as the length of its cephalon. It has been hypothesized that this large doublure could have aided the animal in digging through sediment to find food, as it was thought to have been both a predator of small animals and a scavenger. ''Squamacula clypeata'' has one pair of antennae attached to its cephalon, but no other appendages or auditory or visual structures. No mouth is present in the specimens, but the gut is present, so ''S. clypeata'' must have had a mouth, which is thought to have been between the cephalon and doublure on the underside. ''Squamacula clypeata'' has one pair of [biramous](/source/biramous) appendages (an appendage which branches into two) per thoracic tergite. The [endopod](/source/endopod) (inside branch) has seven segments, the first six of which are roughly even in size and shape, with small spines on the underside, and the last of which terminates with a claw and appears to have been used for walking and eating, as the claw could be useful in grabbing hold of and tearing up food. The exopod (outside branch) was not segmented, but flap-like, with [seta](/source/seta)e (bristles) near the tip, which may have been used for both locomotion and respiration. ''S. buckorum'' differs from ''S. clypeata'' in that it has 11 thoracic tergites, which appear to exhibit less overlap that those of ''S. clypeata,'' though the differences between the two species are relatively minor. The species also preserves elements of the gut tract not preserved in ''S. clypeata'', which show that it was narrow annulated tube running along the midline of the animal, with three or possibly four pairs of midgut glands within the cephalic shield, with other gland pairs extending along the trunk. == Taxonomy == In phylogenetic analyses, ''Squamacula'' has consistently been placed as the earliest diverging and most primitive member of [Artiopoda](/source/Artiopoda), a clade that includes [trilobite](/source/trilobite)s and a variety of morphologically similar soft-bodied forms.{{Cite journal |last1=Jiao |first1=De-Guang |last2=Du |first2=Kun-Sheng |last3=Zhang |first3=Xi-Guang |last4=Yang |first4=Jie |last5=Eggink |first5=Daniel |date=May 2022 |title=A new small soft-bodied non-trilobite artiopod from the Cambrian Stage 4 Guanshan Biota |journal=Geological Magazine |language=en |volume=159 |issue=5 |pages=730–734 |doi=10.1017/S0016756821001254 |bibcode=2022GeoM..159..730J |issn=0016-7568|doi-access=free }} A close relationship has been proposed with the genus ''[Thulaspis](/source/Thulaspis)'' from the [Sirius Passet](/source/Sirius_Passet) site of Greenland.{{Cite journal |last1=Berks |first1=Harry O. |last2=Lunde Nielsen |first2=Morten |last3=Flannery‐Sutherland |first3=Joseph |last4=Thorshøj Nielsen |first4=Arne |last5=Park |first5=Tae‐Yoon S. |last6=Vinther |first6=Jakob |date=May 2023 |title=A possibly deep branching artiopodan arthropod from the lower Cambrian Sirius Passet Lagerstätte (North Greenland) |journal=Papers in Palaeontology |language=en |volume=9 |issue=3 |doi=10.1002/spp2.1495 |issn=2056-2799|doi-access=free }} Implied weights parsimony phylogeny after Berks et al. 2023.{{Cite journal |last1=Berks |first1=H. O. |last2=Nielsen |first2=M. L. |last3=Flannery-Sutherland |first3=J. |last4=Nielsen |first4=A. T. |last5=Park |first5=T.-Y. S. |last6=Vinther |first6=J. |year=2023 |title=A possibly deep branching artiopodan arthropod from the lower Cambrian Sirius Passet Lagerstätte (North Greenland) |journal=Papers in Palaeontology |volume=9 |issue=3 |at=e1495 |doi=10.1002/spp2.1495 |s2cid=259253098 |doi-access=free}}{{clade|{{clade |1={{clade |1=''[Thulaspis](/source/Thulaspis)'' 100px |2=''Squamacula'' 80px }} |2={{clade |label1=Protosutura |1={{clade |1=''[Zhiwenia](/source/Zhiwenia)'' 50px |2=''[Australimicola](/source/Australimicola)'' 35px |3=''[Acanthomeridion](/source/Acanthomeridion)'' 100px }} |2={{clade |label1=[Vicissicaudata](/source/Vicissicaudata) |1={{clade |1=''[Sidneyia](/source/Sidneyia)'' 100px |2={{clade |1=[Cheloniellida](/source/Cheloniellida) 70px |2={{clade |1=''[Emeraldella](/source/Emeraldella)'' 70px |2={{clade |1=''[Kodymirus](/source/Kodymirus)'' 70px |2={{clade |1=''[Eozetetes](/source/Eozetetes)'' |2=[Aglaspidida](/source/Aglaspidida) 100px }}}}}}}}}} |label2=[Trilobitomorpha](/source/Trilobitomorpha) |2={{clade |1={{clade |1=''[Retifacies](/source/Retifacies)'' 100px |2=''[Pygmaclypeatus](/source/Pygmaclypeatus)'' 100px }} |2={{clade |1=[Xandarellida](/source/Xandarellida) 70px |2={{clade |1=[Nektaspida](/source/Nektaspida) 70px |2={{clade |1=[Conciliterga](/source/Conciliterga) 100px |2={{clade |1=''[Kwanyinaspis](/source/Kwanyinaspis)'' 70px |2={{clade |1=''[Phytophilaspis](/source/Phytophilaspis)'' 70px |2=[Trilobita](/source/Trilobita) 100px }}}}}}}}}}}}}}}}}}|label1=[Artiopoda](/source/Artiopoda)}} == References == {{Reflist}} {{Artiopoda}} {{Taxonbar|from=Q85802772}} Category:Artiopoda Category:Artiopod genera --- Adapted from the Wikipedia article [Squamacula](https://en.wikipedia.org/wiki/Squamacula) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Squamacula?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.