Cephalodiscus

{{Short description|Genus of hemichordates}} {{Automatic taxobox | fossil_range = Cambrian (Miaolingian, ?Wuliuan)–Present<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'' | image2 = Cephalodiscus planitectus - Examples of the Hemichordata (cropped).jpg | image2_caption = Ventral view of a zooid of ''Cephalodiscus planitectus'' | taxon = Cephalodiscus | authority = 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'' | type_species_authority = McIntosh, 1882 | subdivision_ranks = Species | subdivision = See text | synonyms = * ''Demiothecia'' Ridewood, 1906 * ''Idiothecia'' Ridewood, 1906 * ''Orthoecus'' Andersson, 1907 * ''Acoelothecia'' John, 1931 }}

'''''Cephalodiscus''''' is a genus of hemichordates in the family Cephalodiscidae of the order Cephalodiscida.

==Description== All known species live in a secreted coenecium attached to a rock substrate.<ref name=MReview /> Unlike ''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. ''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'' Harmer & Ridewood, 1914 * ''Cephalodiscus atlanticus'' Bayer, 1962 * ''Cephalodiscus australiensis'' Johnston & Muirhead, 1951 * ''Cephalodiscus calciformis'' Emig, 1977 * ''Cephalodiscus densus'' Andersson 1907 [''Cephalodiscus rarus'' Andersson, 1907; ''Cephalodiscus anderssoni'' Gravier 1912] * ''Cephalodiscus dodecalophus'' McIntosh 1882 * ''Cephalodiscus evansi'' Ridewood * ''Cephalodiscus fumosus'' John, 1932 * ''Cephalodiscus gilchristi'' Ridewood, 1908 * ''Cephalodiscus gracilis'' Harmer 1905 * ''Cephalodiscus graptolitoides'' Dilly 1993 * ''Cephalodiscus hodgsoni'' Ridewood, 1907 [''Cephalodiscus aequatus'' Andersson 1907; ''Cephalodiscus inaequatus'' Andersson 1907] * ''Cephalodiscus indicus'' Schepotieff 1909 * ''Cephalodiscus kempi'' John, 1932 * ''Cephalodiscus levinsoni'' Harmer 1905 * ''Cephalodiscus nigrescens'' Lankester 1905 * ''Cephalodiscus planitectus'' Miyamoto, Nishikawa and Namikawa, 2020 * ''Cephalodiscus sibogae'' Harmer 1905 * ''Cephalodiscus solidus'' Andersson, 1907

Extinct species include: * †''Cephalodiscus lutetianus'' Abrard, Dollfus & Soyer 1950 * †''Cephalodiscus nusplingensis'' Schweigert & Dietl 2013

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

==Historical discovery== ''Cephalodiscus'' are endemic to the Antarctic and Southern Ocean, whose relative inaccessibility has historically limited human study of the genus.<ref name=MReview /> The ''Erebus'' and ''Terror'' may have unwittingly encountered ''C. nigrescens'' specimens, and the ''Challenger'' ''C. densus''; but until the Swedish Antarctic Expedition of 1901-1903, only ''C. dodecalphus'' had been identified.<ref name=RKerg /> In 1882, William M'Intosh (later spelled McIntosh) had identified ''Dodecalphus'' from dredged 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)|last=Markham|first=John C.|chapter=The Species of ''Cephalodiscus'' collected during Operation Deep Freeze, 1956-1959|pages=83-110|via=the 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 A.|editor-last2=Wallen|editor-first2=I. Eugene|year=1971|isbn=0-87590-117-4}}</ref><ref name=RKerg>{{Cite journal |last=Ridewood |first=W. 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}}</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, the Falklands, Sri Lanka, and Australia. At the same time, researchers also determined that ''C. rarus'' and ''andersonii'' were in fact ''C. densus'' specimens.<ref name=MReview />

''Cephalodiscus planitectus'' is the most recently discovered species. It was described in 2020 from specimens found in Sagami Bay off the southern coast of 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''}}

Category:Cephalodiscus Category:Hemichordate genera Category:Pterobranchia