# Cephalodiscus

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{{Short description|Genus of hemichordates}}
{{Automatic taxobox
| fossil_range = [Cambrian](/source/Cambrian) ([Miaolingian](/source/Miaolingian), ?[Wuliuan](/source/Wuliuan))–[Present](/source/Holocene)<ref name=Treatise>{{Cite journal |last=Maletz |first=Jörg |last2=Gonzalez |first2=Paul |date=2017-02-15 |title=Treatise Online no. 100: Part V, Second Revision, Chapter 14: Order Cephalodiscida: Introduction and systematic descriptions |url=https://journals.ku.edu/treatiseonline/article/view/6674 |journal=Treatise Online |language=en |doi=10.17161/to.v0i0.6674 |issn=2153-4012}}</ref>{{Geological range|Wuliuan|0|}}
| image = Cephalodiscus dodecalophus McIntosh.png
| image_caption = ''[Cephalodiscus dodecalophus](/source/Cephalodiscus_dodecalophus)''
| image2 = Cephalodiscus planitectus - Examples of the Hemichordata (cropped).jpg
| image2_caption = Ventral view of a zooid of ''[Cephalodiscus planitectus](/source/Cephalodiscus_planitectus)''
| taxon = Cephalodiscus
| authority = [M'Intosh](/source/William_M'Intosh), 1882<ref>M'Intosh W (1882) Preliminary notice of ''Cephalodiscus'', a new type allied to Prof. Allman's ''Rhabdopleura'' dredged in H.M.S. 'Challenger.'. ''Annals and Magazine of Natural History'' 10: 337-348</ref>
| type_species = ''[Cephalodiscus dodecalophus](/source/Cephalodiscus_dodecalophus)''
| type_species_authority =  McIntosh, 1882
| subdivision_ranks = Species
| subdivision = See text
| synonyms = 
* ''Demiothecia'' <small>Ridewood, 1906</small>
* ''Idiothecia'' <small>Ridewood, 1906</small>
* ''Orthoecus'' <small>Andersson, 1907</small>
* ''Acoelothecia'' <small>John, 1931</small>
}}

'''''Cephalodiscus''''' is a genus of [hemichordate](/source/hemichordate)s in the family [Cephalodiscidae](/source/Cephalodiscidae) of the order [Cephalodiscida](/source/Cephalodiscida).

==Description==
All known species live in a secreted coenecium attached to a rock substrate.<ref name=MReview />  Unlike ''[Rhabdopleura](/source/Rhabdopleura)'', ''Cephalodiscus'' species do not form large colonies and are only pseudocolonial, but they do share a common area with individual buds for each zooid.<ref name=MReview /><ref name= Maletzgp />  ''Cephalodiscus'' zooids are also more mobile than their ''Rhabdopleura'' counterparts, and are able to move around within [tubaria](/source/tubarium). ''Cephalodiscus'' zooids can be produced via asexual budding. There are a few pairs of tentacled arms, whereas ''Rhabdopleura'' has only one pair of arms.<ref name= Maletzgp>{{cite book|last=Maletz|first=Jörg|title=Graptolite Paleobiology|year=2017|publisher=Wiley-Blackwell|url=https://www.wiley.com/en-us/Graptolite+Paleobiology-p-9781118515617|isbn=9781118515617}}</ref>  

==Species==
19 living species of ''Cephalodiscus'' have been described:<ref>{{WoRMS||id=264904|title=''Cephalodiscus''}}</ref>
* ''[Cephalodiscus agglutinans](/source/Cephalodiscus_agglutinans)'' <small>Harmer & Ridewood, 1914</small>
* ''[Cephalodiscus atlanticus](/source/Cephalodiscus_atlanticus)'' <small>Bayer, 1962</small>
* ''[Cephalodiscus australiensis](/source/Cephalodiscus_australiensis)'' <small>Johnston & Muirhead, 1951</small>
* ''[Cephalodiscus calciformis](/source/Cephalodiscus_calciformis)'' <small>Emig, 1977</small>
* ''[Cephalodiscus densus](/source/Cephalodiscus_densus)'' <small>Andersson 1907</small> [''Cephalodiscus rarus'' <small>Andersson, 1907</small>; ''Cephalodiscus anderssoni'' <small>Gravier 1912</small>]
* ''[Cephalodiscus dodecalophus](/source/Cephalodiscus_dodecalophus)'' <small>McIntosh 1882</small>
* ''[Cephalodiscus evansi](/source/Cephalodiscus_evansi)'' <small>Ridewood</small>
* ''[Cephalodiscus fumosus](/source/Cephalodiscus_fumosus)'' <small>John, 1932</small>
* ''[Cephalodiscus gilchristi](/source/Cephalodiscus_gilchristi)'' <small>Ridewood, 1908</small>
* ''[Cephalodiscus gracilis](/source/Cephalodiscus_gracilis)'' <small>Harmer 1905</small>
* ''[Cephalodiscus graptolitoides](/source/Cephalodiscus_graptolitoides)'' <small>Dilly 1993</small>
* ''[Cephalodiscus hodgsoni](/source/Cephalodiscus_hodgsoni)'' <small>Ridewood, 1907</small> [''Cephalodiscus aequatus'' <small>Andersson 1907</small>; ''Cephalodiscus inaequatus'' <small>Andersson 1907</small>]
* ''[Cephalodiscus indicus](/source/Cephalodiscus_indicus)'' <small>Schepotieff 1909</small>
* ''[Cephalodiscus kempi](/source/Cephalodiscus_kempi)'' <small>John, 1932</small>
* ''[Cephalodiscus levinsoni](/source/Cephalodiscus_levinsoni)'' <small>Harmer 1905</small>
* ''[Cephalodiscus nigrescens](/source/Cephalodiscus_nigrescens)'' <small>Lankester 1905</small>
* ''[Cephalodiscus planitectus](/source/Cephalodiscus_planitectus)'' <small>Miyamoto, Nishikawa and Namikawa, 2020</small>
* ''[Cephalodiscus sibogae](/source/Cephalodiscus_sibogae)'' <small>Harmer 1905</small>
* ''[Cephalodiscus solidus](/source/Cephalodiscus_solidus)'' <small>Andersson, 1907</small>

Extinct species include:
* †''[Cephalodiscus lutetianus](/source/Cephalodiscus_lutetianus)'' <small>Abrard, Dollfus & Soyer 1950</small>
* †''[Cephalodiscus nusplingensis](/source/Cephalodiscus_nusplingensis)'' <small>Schweigert & Dietl 2013</small>

Proposed subgenera are ''Idiothecia'', ''Demiothecia'', ''Orthoecus'', and ''Acoelothecia''.<ref name=MReview />  

==Historical discovery==
''Cephalodiscus'' are [endemic](/source/Endemism) to the [Antarctic](/source/Antarctic) and [Southern Ocean](/source/Southern_Ocean), whose relative inaccessibility has historically limited human study of the genus.<ref name=MReview />  The [''Erebus'' and ''Terror''](/source/Ross_expedition) may have unwittingly encountered ''C. nigrescens'' specimens, and the [''Challenger''](/source/HMS_Challenger) ''C. densus''; but until the [Swedish Antarctic Expedition](/source/Swedish_Antarctic_Expedition) of 1901-1903, only ''C. dodecalphus'' had been identified.<ref name=RKerg />  In 1882, [William M'Intosh](/source/William_M'Intosh) (later spelled McIntosh) had identified ''Dodecalphus'' from [dredged](/source/Dredging) [Magellanic-Straits](/source/Magellanic_Straits) material, work published 5 years later, but the discovery left cephalodiscid phylogeny unclear.<ref name=MReview>{{cite book|title=Biology of the Antarctic Seas|volume=17 (IV)<!--the series includes works with other titles, so that volume 17 is "Biology of the Antarctic Seas IV"-->|last=Markham|first=John&nbsp;C.|chapter=The Species of ''Cephalodiscus'' collected during Operation Deep Freeze, 1956-1959|pages=83-110|via=the [Internet Archive](/source/Internet_Archive)|chapter-url=https://archive.org/details/biologyofantarct0000unse_r0w3/page/82/|series=Antarctic Research|publisher=Horn-Shafer|place=Baltimore|editor-last1=Llano|editor-first1=George&nbsp;A.|editor-last2=Wallen|editor-first2=I.&nbsp;Eugene|year=1971|isbn=0-87590-117-4}}</ref><ref name=RKerg>{{Cite journal |last=Ridewood |first=W.&nbsp;G. |date=October 1921 |title=On specimens of ''Cephalodiscus densus'' dredged by the ‘Challenger’ in 1874 at Kerguelen Island |url=https://www.biodiversitylibrary.org/partpdf/63792 |format=PDF |journal=Annals and Magazine of Natural History |language=en |volume=8 |issue=46 |pages=433–440 |doi=10.1080/00222932108632603 |issn=0374-5481 |via=[Biodiversity Heritage Library](/source/Biodiversity_Heritage_Library)}}</ref>  M'Intosh proposed placement amongst the polyzoa, whilst Harmer suggested the modern placement amongst hemichordates.  The Swedish expedition provided a plethora of new species, and subsequent researchers began to recognize cephalodiscid species in the relatively temperate waters off [South Africa](/source/South_Africa), the [Falklands](/source/Falklands), [Sri Lanka](/source/Sri_Lanka), and [Australia](/source/Australia).  At the same time, researchers also determined that ''C. rarus'' and ''andersonii'' were in fact ''C. densus'' specimens.<ref name=MReview /> 

''[Cephalodiscus planitectus](/source/Cephalodiscus_planitectus)'' is the most recently discovered species. It was described in 2020 from specimens found in [Sagami Bay](/source/Sagami_Bay) off the southern coast of [Honshu](/source/Honshu), Japan.<ref name="Miyamoto">{{cite journal |vauthors=Miyamoto N, Nishikawa T, Namikawa H |title=''Cephalodiscus planitectus'' sp. nov. (Hemichordata: Pterobranchia) from Sagami Bay, Japan |journal=Zoological Science |volume=37 |issue=1 |pages=79–90 |date=February 2020 |pmid=32068377 |doi=10.2108/zs190010 |url=https://bioone.org/journals/zoological-science/volume-37/issue-1/zs190010/Cephalodiscus-planitectus-sp-nov-Hemichordata--Pterobranchia-from-Sagami-Bay/10.2108/zs190010.short |access-date=2020-09-17|url-access=subscription }}</ref>

==References==
{{Reflist}}

==External links==
* {{Wikispecies-inline}}
* {{WoRMS||id=264904|title=''Cephalodiscus''}}

{{Taxonbar|from=Q3830429}}

Category:Cephalodiscus
Category:Hemichordate genera
Category:Pterobranchia

{{Hemichordate-stub}}

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Adapted from the Wikipedia article [Cephalodiscus](https://en.wikipedia.org/wiki/Cephalodiscus) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Cephalodiscus?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.