| 词条 | Acimetopus |
| 释义 |
| name = Acimetopus | fossil_range = {{Geological range|522|516|Botomian (Olenellus-zone)}} | image = Acimetopus linedrawing.jpg | image_upright = 0.6 | image_caption = Acimetopus bilobatus | regnum = Animalia | phylum = Arthropoda | classis = Trilobita | ordo = Agnostida | familia = Weymouthiidae | genus = Acimetopus | genus_authority = Rasetti, 1966 | type_species = Acimetopus bilobatus | type_species_authority = Rasetti, 1966 [1] }}Acimetopus is a genus of trilobites that lived during the Botomian stage.[1] DistributionAcimetopus is known from the Lower Cambrian of the United States (unnamed formation, East Chatham Quad, Columbia County, New York State {{Coord|42|24|N|73|30|W}}),[2] and England.[4]DescriptionLike in all Agnostida, the body of Acimetopus is diminutive, the headshield (or cephalon) and tailshield (or pygidium) are approximately the same size (or isopygious). The thorax is unknown but all weymouthiids where it is known have 3 thoracic segments. Acimetopus has no eyes. Its cephalic border is strongly convex, with a pair of lateral marginal spines. The entire exoskeleton of Acimetopus is covered in granules. The central raised area of the cephalon, called the glabella, is strongly divided by two deep furrows that merge when crossing the midline. The large and inflated anterior lobe is isolated from border furrow. Behind it is a pair of small, separated, subtriangular lobes. The posterior part of the glabella is large and carries an inflated spine that is directed upwards and backwards. Genal spines are present. The axis of the pygidium (or rhachis) has nine rings that are strongly inflated, with the second ring carrying a vertical spine. The border surrounding the pygidium is defined by a deep furrow, is narrow, and lacks spines.[3] EcologyAcimetopus bilobatus occurs in association with other Weymouthiidae (Acidiscus, Analox, Bathydiscus, Bolboparia, Leptochilodiscus, Serrodiscus), Calodiscus, several species of Olenellus and Bonnia (Dorypygidae).[2]References1. ^1 {{cite journal|last=Sepkoski |first=Jack |title=A compendium of fossil marine animal genera (Trilobita entry) |journal=Bulletins of American Paleontology |volume=364 |page=560 |year=2002 |url=http://strata.ummp.lsa.umich.edu/jack/showgenera.php?taxon=307&rank=class |accessdate=12 January 2008 |deadurl=yes |archiveurl=https://web.archive.org/web/20060905162524/http://strata.ummp.lsa.umich.edu/jack/showgenera.php?taxon=307&rank=class |archivedate=5 September 2006 }} {{Taxonbar|from=Q4674155}}{{agnostida-stub}}2. ^1 {{cite web|author=Paleobiology Database|title= East Chatham Quad, unnamed fm., NY (Cambrian of the United States) (trilobite)|accessdate= 19 December 2012|url=http://paleodb.org/cgi-bin/bridge.pl?a=basicCollectionSearch&collection_no=189}} 3. ^1 {{Cite book|last= Whittington|first= H. B.|year= 1997|title= Treatise on Invertebrate Paleontology. Part O, Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida}} 7 : Weymouthiidae|Agnostida genera|Cambrian trilobites of Europe|Fossils of the United Kingdom|Fossils of the United States|Animals described in 1966|Cambrian trilobites of North America |
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