View source for Acmarhachis

{{italic title}}
{{Taxobox
| fossil_range = {{Fossil range|Upper Cambrian}}
| regnum = [[Animal]]ia
| phylum = [[Arthropod]]a
| classis = [[Trilobite|Trilobita]]
| ordo = [[Agnostida]]
| subordo = [[Agnostoidea]]
| familia = [[Agnostidae]]
| subfamilia = [[Incertae sedis|incertae subfamiliae]]
| genus='''''Acmarhachis'''''
| genus_authority = Resser, 1938
| synonyms = ''Cyclagnostus'', ''Wanagnostus''
| subdivision_ranks = [[Species]]
| subdivision = 
* ''A. typicalis'' <small>Resser, 1938 ([[Type (biology)|type]])</small> 
* ''A. acuta'' <small>(Kobayashi, 1938)</small>
* ''A. anhuiensis'' <small>(Qiu, 1983)</small> [[Synonym (taxonomy)|synonym]] ''Wanagnostus anhuiensis''
* ''A. apicula'' <small>[[Armin Öpik|Öpik]], 1967</small> synonym ''Oxyagnostus apicula''
* ''A. elegans'' <small>([[Ekaterina Lermontova|Lermontova]], 1940)<ref>Arthropoda - Klass trilobity (Class Trilobita). EV Lermontova, Atlas of the Leading Forms of the Fossil Faunas of the USSR, 1940</ref></small> synonym ''Cyclagnostus elegans'' Lerm., 1940
* ''A. karatauensis'' <small>Ergaliev, 1980</small> 
* ''A. longispinus'' <small>Ergaliev, 1980</small> 
* ''A. punctatus'' <small>Ergaliev, 1980</small>
* ''A. whittingtoni'' <small>Westrop & Eoff, 2012</small><ref name='Treatise'>Whittington, H. B. et al. Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997</ref>
}}
'''''Acmarhachis''''' is a genus of [[trilobite]] in the order [[Agnostida]], which lived in what are now Australia (Queensland, Tasmania), Canada (British Columbia, Newfoundland, Northwest Territories), China (Anhui), Kazakhstan, Russia (Kharaulakh), and the US (Alaska, Alabama, Nevada, Maryland, Vermont). It was described by Resser in 1938, and the type species is ''Acmarhachis typicalis''.<ref>[http://www.trilobites.info/generic_names_Jell%26Adrain2003.pdf Available Generic Names for Trilobites] P.A. Jell and J.M. Adrain.</ref>

== Distribution ==
* ''A. typicalis'' occurs in the Cambrian of Kazakhstan (Kyrshabakty River, ''Lejopyge laevigata''-trilobite zone, Zhumabai Formation, Paibian and Cambrian Stage 9, 43.5° N, 70.0° E).<ref>{{cite book|last1= Ergaliev|first1= G.K.|last2= Ergaliev|first2= F.G.|year= 2008|title= Agnostidy srednego i verkhnego Kembriya Aksayskogo Gosudarstvennogo Geologicheskogo Zakaznika v yushnom Kazakhstane (Kyrshabakty, Malyy Karatau) [Middle and Upper Cambrian Agnostida from the Aksai National Geological Reserve in southern Kazakhstan (Kyrshabakty River, Malyy Karatau Range)]|pages= 1–359}} ''cited in'' {{cite web|author= Paleobiological Database|title= Acmarhachis whittingtoni|accessdate= 25 October 2013|url= http://fossilworks.org/cgi-bin/bridge.pl?a=taxonInfo&taxon_no=203567}}</ref><!---other country data from PBDB still have to be added--->
* ''A. whittingtoni'' is known from the Upper Cambrian of Canada (Hickey Cove, ''Dunderbergia''-trilobite zone, Downes Point Member, Shallow Bay Formation, Paibian, Newfoundland, 49.8° N, 57.9° W).<ref>{{cite journal|last1= Westrop|first1= S.R.|last2= Eoff|first2= .J.D.|year= 2012|title= Late Cambrian (Furongian; Paibian, Steptoean) agnostoid arthropods from the Cow Head Group, western Newfoundland|journal= Journal of Paleontology|volume= 86|issue= 2|pages= 201–237|doi=10.1666/11-034.1}} ''cited in'' {{cite web|author= Paleobiological Database|title= Acmarhachis whittingtoni|accessdate= 25 October 2013|url= http://fossilworks.org/cgi-bin/bridge.pl?taxon_no=234822&action=basicTaxonInfo}}</ref>

== Description ==
Like all Agnostida, ''Acmarhachis'' is diminutive and the headshield (or [[Cephalon (arthropod head)#Trilobites|cephalon]]) and tailshield (or [[pygidium]]) are of approximately the same size (or [[Pygidium#Trilobites|isopygous]]) and outline. As in all Agnostina, ''Acmarhachis'' has two [[thorax]] segments. When Agnostina are enroled, a tiny opening between the cephalon and the thorax becomes visible (the cephalothoracic aperture) that uniquely distinguishes this group from the [[Eodiscina]]. A feature shared with all Agnostoidea is that the frontal lobe of the central raised area of the cephalon (or glabella) is not laterally expanded compared to the backward lobe, like in the [[Condylopygoidea]]. In ''Acmarhachis'' the furrow at midline between the front of the glabella and the border is weak or absent. The glabella has a long [[Ogive|ogival]] to [[Rectangle|subquadrate]] front lobe, and the furrow defining it at its back is straight. The back lobe of the glabella is accompanied by two triangular basal lobes of moderate to large size. On the pygidium the axis or rhachis reaches the border. It is divided along its length in three lobes. It is shaped a bit like an [[amphora]], the back pointed and strongly constricted across the middle lobe. The middle lobe also carries a node where it contacts the posterior lobe.<ref name='Treatise'/>

==References==
{{reflist}}

[[Category:Agnostida]]
[[Category:Cambrian trilobites of Australia]]
[[Category:Fossils of British Columbia]]
[[Category:Fossils of Kazakhstan]]
[[Category:Cambrian trilobites of North America]]
[[Category:Cambrian trilobites of Asia]]
[[Category:Paleontology in Newfoundland and Labrador]]
[[Category:Paleontology in the Northwest Territories]]