View source for Helmetia

{{Short description|Genus of arthropods (fossil)}}
{{Speciesbox
| fossil_range = Cambrian
| image = Helmetia expansa.jpg
| image_caption = Artist's rendition of Helmetia alongside [[Tegopelte gigas]]
| genus = Helmetia
| species = expansa
| authority = Walcott, 1918
| display_parents = 3
}}
'''''Helmetia''''' is an [[extinct]] [[genus]] of [[arthropod]] from the middle [[Cambrian]]. Its fossils have been found in the [[Burgess Shale]] of Canada and the Jince Formation of the [[Czech Republic]].<ref>{{cite journal |author=Kordule Chlupáč |year=2002 |title=Arthropods of Burgess Shale type from the Middle Cambrian of Bohemia (Czech Republic) |journal=Bulletin of the Czech Geological Survey |volume=77 |pages=167–182}}</ref>
Fossils are both rare and poorly known; the genus was described by Walcott in 1918 and has not been reexamined, though it was briefly reviewed in the 1990s and has been included in a number of cladistic analyses. It has been lumped with the [[Arachnomorpha|arachnomorphs]]. One analysis has resolved the Helmetiiida as a robust clade and the closest relatives of trilobites.<ref>{{Cite journal|last1=Edgecombe|first1=Gregory D.|last2=Ramsköld|first2=Lars|date=1999|title=Relationships of Cambrian Arachnata and the Systematic Position of Trilobita|journal=Journal of Paleontology|volume=73|issue=2|pages=263–287|jstor=1306784|doi=10.1017/S0022336000027761|bibcode=1999JPal...73..263E |s2cid=84029615 }}</ref>
The most complete specimen of ''Helmetia'' is 19&nbsp;cm long, and has six thoracic segments. There is a head shield and a large tail shield, making the animal leaf-shaped. Unlike trilobites, the margin of the head shield is concave, ending in a spine on each corner. There is an oval structure with two spots at the anterior center of the head shield, behind which are two eyes. The whole animal is broad and flat with a thin exoskeleton. The central region shows paired muscle scars and filamentous structures interpreted as limbs. Because the head shield, thoracic segments, and tail shield are all angular in outline and end in spines, ''Helmetia'' is unstreamlined and would likely be a slow swimmer. However, the flattened body and filamentous limbs suggest a floating or swimming lifestyle.<ref>{{Cite web|url=https://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=65&m=2&|title=The Burgess Shale|last=Canada|first=Royal Ontario Museum and Parks|date=2011-06-10|website=burgess-shale.rom.on.ca|language=en|access-date=2018-10-28}}{{Dead link|date=July 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> It has been interpreted as a nektonic suspension feeder.<ref>CARON, J.-B. and JACKSON, D. A. 2008. Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258, 222–256.</ref>
== References ==
{{Reflist}}
== Further reading ==
* {{cite book |title=Wonderful Life: The Burgess Shale and the Nature of History |author=Stephen Jay Gould |author-link=Stephen Jay Gould |year=1989 |publisher=[[W. W. Norton & Company]]|title-link=Wonderful Life (book) |bibcode=1989wlbs.book.....G }}
* {{cite book |title=The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life |author=Xian-Guang Hou |author2=Richard J. Aldridge |author3=Jan Bergström|author4=David J. Siveter|author4-link=David J. Siveter |author5=Derek J. Siveter |author6=Feng Xiang-Hong |name-list-style=amp |publisher=[[John Wiley & Sons]] |year=2004 |isbn=978-1-4051-0673-3}}
== External links ==
* {{Cite web|date=2011|title=''Helmetia expansa''|work=Burgess Shale Fossil Gallery|publisher=Virtual Museum of Canada|url=http://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=65|archive-url=https://web.archive.org/web/20201112025257/http://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=65|archive-date=2020-11-12|url-status=dead|access-date=2023-01-21}}
*[https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=19037 ''Helmetia''] in the [[Paleobiology Database]]
{{Artiopoda}}
{{Taxonbar|from=Q3784705}}
[[Category:Prehistoric chelicerates]]
[[Category:Cambrian arthropods]]
[[Category:Prehistoric animals of Europe]]
[[Category:Burgess Shale fossils]]
[[Category:Fossil taxa described in 1918]]
[[Category:Cambrian genus extinctions]]
[[Category:Artiopoda]]
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