Editing Hemichordate (section)

== Classification ==
{{See also|List of bilateral animal orders}}
[[File:DiplograptusCaneySprings.jpg|thumb|right|''Amplexograptus'', a [[graptolite]] hemichordate, from the [[Ordovician]] near [[Caney Springs, Tennessee|Caney Springs]], [[Tennessee]].]]

Hemichordata are divided into two classes: the [[Acorn worm|Enteropneusta]],<ref>{{Cite journal | last1 = Cameron | first1 = CB | last2 = Garey | first2 = JR | author3-link = Billie J. Swalla | last3 = Swalla | first3 = BJ | title = Evolution of the chordate body plan: new insights from phylogenetic analyses of deuterostome phyla | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 97 | issue = 9 | pages = 4469–74 | date = 25 April 2000 | pmid = 10781046 | pmc = 18258 |bibcode = 2000PNAS...97.4469C |doi = 10.1073/pnas.97.9.4469 | doi-access = free }}</ref> commonly called acorn worms, and the [[Pterobranchia]], which includes the [[graptolite]]s.<ref name="Rhabdopleura2020">{{cite journal |last1=Ramírez-Guerrero |first1=G. M. |last2=Kocot, K. M. |last3=Cameron |first3=C. B. |year=2020 |title=Zooid morphology and molecular phylogeny of the graptolite ''Rhabdopleura annulata'' (Hemichordata, Pterobranchia) from Heron Island, Australia |journal=Canadian Journal of Zoology |volume=98 |issue=12 |pages=844–849|doi=10.1139/cjz-2020-0049 |s2cid=228954598 }}</ref> A third class, [[Planctosphaeroidea]], is proposed based on a single species known only from larvae. The phylum contains about 120 living species.<ref name=Zhang2011>{{cite journal| author=Zhang, Z.-Q.| title=Animal biodiversity: An introduction to higher-level classification and taxonomic richness | journal=Zootaxa| volume=3148| year=2011| pages=7–12| url=http://mapress.com/zootaxa/2011/f/zt03148p012.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://mapress.com/zootaxa/2011/f/zt03148p012.pdf |archive-date=2022-10-09 |url-status=live| doi=10.11646/zootaxa.3148.1.3 }}</ref> Hemichordata appears to be sister to the Echinodermata as Ambulacraria; Xenoturbellida may be basal to that grouping. Pterobranchia may be derived from within Enteropneusta, making Enteropneusta paraphyletic. It is possible that the extinct organism ''[[Etacystis]]'' is a member of the Hemichordata, either within or with close affinity to the Pterobranchia.<ref>{{cite journal |url=http://jpaleontol.geoscienceworld.org/content/50/6/1157.short |title=Etacystis communis, a Fossil of Uncertain Affinities from the Mazon Creek Fauna (Pennsylvanian of Illinois) |journal=[[Journal of Paleontology]] |volume=50 |date= November 1976 |pages=1157–1161}}</ref>

There are 130 described species of Hemichordata and many new species are being discovered, especially in the deep sea.<ref name=Tassia2016>{{cite journal | last1 = Tassia | first1 = MG | last2 = Cannon | first2 = JT | last3 = Konikoff | first3 = CE | last4 = Shenkar | first4 = N | last5 = Halanych | first5 = KM | author6-link = Billie J. Swalla | last6 = Swalla | first6 = BJ | year = 2016 | title = The Global Diversity of Hemichordata | journal = PLOS ONE | volume = 11 | issue = 10| page = e0162564 | doi = 10.1371/journal.pone.0162564 | pmid=27701429 | pmc=5049775| bibcode = 2016PLoSO..1162564T | doi-access = free }}</ref>

===Phylogeny===
A [[phylogenetic tree]] showing the position of the hemichordates is:

{{clade
|1={{clade
   |label1=[[Chordata]]
   |1={{clade
      |1=[[Cephalochordata]] [[File:Branchiostoma lanceolatum (Pallas, 1774).jpg|80 px]]
      |label2=[[Olfactores]]
      |2={{clade
         |1=[[Tunicata]] [[File:Tunicate komodo.jpg|60 px]]
         |2=[[Vertebrate|Vertebrata]]/[[Craniata]] [[File:Common carp (white background).jpg|60 px]] 
         }}
      }}
   |label2=[[Ambulacraria]]
   |2={{clade
      |1=[[Echinodermata]] [[File:Portugal 20140812-DSC01434 (21371237591).jpg|60 px]]
      |2='''Hemichordata''' [[File:Saccoglossus kowalevskii by Spengel 1893.png|50 px]]
      }}
   }}|label1=[[Deuterostomia]]|style=font-size:80%; line-height:80%}}

The internal relationships within the hemichordates are shown below. The tree is based on 16S +18S rRNA sequence data and phylogenomic studies from multiple sources.<ref>{{Cite journal |last1=Tassia |first1=Michael G. |last2=Cannon |first2=Johanna T. |last3=Konikoff |first3=Charlotte E. |last4=Shenkar |first4=Noa |last5=Halanych |first5=Kenneth M. |author6-link=Billie J. Swalla |last6=Swalla |first6=Billie J. |date=2016-10-04 |title=The Global Diversity of Hemichordata |journal=PLOS ONE |volume=11 |issue=10 |pages=e0162564 |doi=10.1371/journal.pone.0162564 |pmid=27701429 |pmc=5049775|bibcode=2016PLoSO..1162564T |doi-access=free }}</ref><ref>{{Cite journal|last1=Halanych|first1=Kenneth M.|last2=Bernt|first2=Matthias|last3=Cannon|first3=Johanna T.|last4=Tassia|first4=Michael G.|last5=Kocot|first5=Kevin M.|last6=Li|first6=Yuanning|date=2019-01-01|title=Mitogenomics Reveals a Novel Genetic Code in Hemichordata|journal=Genome Biology and Evolution|language=en|volume=11|issue=1|pages=29–40|doi=10.1093/gbe/evy254|pmc=6319601|pmid=30476024}}</ref><ref name="Maletz">{{cite journal |last=Maletz |first=Jörg| title=The classification of the Pterobranchia (Cephalodiscida and Graptolithina) |journal=Bulletin of Geosciences |year=2014 |volume=89 |issue=3 |pages=477–540 |doi=10.3140/bull.geosci.1465 |issn=1214-1119|doi-access=free }}</ref>

{{clade
|label1='''Hemichordata'''|style=font-size:80%; line-height:80%
|1={{clade
  |label1=[[Enteropneusta]]
  |1={{clade
    |1=''[[Stereobalanus]]''
    |2={{clade
      |1=[[Harrimaniidae]] [[File:Saccoglossus.jpg|60 px]] 
      |2={{clade
        |1=[[Spengeliidae]]
        |label2=
        |2={{clade
          |1=[[Torquaratoridae]]
          |2=[[Ptychoderidae]] [[File:Saccoglossus kowalevskii by Spengel 1893.png|50 px]]
           }}
         }}
       }}
     }}
  |label2=[[Pterobranchia]]
  |2={{clade
    |1=[[Cephalodiscida]] [[File:Cephalodiscus dodecalophus McIntosh.png|50 px]]
    |label2=[[Graptolithina]]
    |2={{clade
      |1=[[Rhabdopleurida]] [[File:Rhabdopleura normani Sedgwick.png|30px]]
      |label2=†[[Eugraptolithina]]
      |2={{clade
        |1=†[[Dendroidea]] [[File:Estonian Museum of Natural History - Dictyonema.png|60px]]
        |2=†[[Graptoloidea]] [[File:Tetragraptus serra (Brongniart).jpg|60px]]
         }}
       }}
     }}
   }}
}}