Cephalodiscus

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

Cephalodiscus
Cephalodiscus dodecalophus
Scientific classification
Kingdom:
Animalia
Phylum:
Hemichordata
Class:
Pterobranchia
Order:
Cephalodiscida
Family:
Cephalodiscidae

Harmer, 1905
Genus:
Cephalodiscus

M'Intosh, 1882[1]
Type species
Cephalodiscus dodecalophus
McIntosh 1882
Species

See text

Synonyms
  • Demiothecia Ridewood 1906
  • (Acoelothecia) John, 1931
  • (Idiothecia) Ridewood 1906
  • (Orthoecus) Andersson 1907

Description

All known species live in a secreted coenecium attached to a rock substrate.[2] 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.[2][3] 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.[3]

Species

19 living species of Cephalodiscus have been described:[4]

Extinct species include:

Proposed subgenera are idiothecia, demiothecia, orthoecus, and acoelothecia.[2]

Historical discovery

The Cephalodisci are endemic to the Antarctic and Southern Ocean, whose relative inaccessibility has historically limited human study of the genus.[2] 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.[5] In 1882, 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.[2][5] 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.[2]

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.[6]

References
  1. 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
  2. Markham, John C. (1971). "The Species of Cephalodiscus collected during Operation Deep Freeze, 1956-1959". In Llano, George A.; Wallen, I. Eugene (eds.). Biology of the Antarctic Seas. Antarctic Research. Vol. 17 (IV). Baltimore: Horn-Shafer. pp. 83–110. ISBN 0-87590-117-4 – via the Internet Archive.
  3. Maletz, Jörg (2017). Graptolite Paleobiology. Wiley-Blackwell. ISBN 9781118515617.
  4. "Cephalodiscus". WoRMS. World Register of Marine Species.
  5. Ridewood, W. G. (October 1921). "On specimens of Cephalodiscus densus dredged by the 'Challenger' in 1874 at Kerguelen Island" (PDF). Annals and Magazine of Natural History. 8 (46): 433–440. doi:10.1080/00222932108632603. ISSN 0374-5481 – via Biodiversity Heritage Library.
  6. Miyamoto N, Nishikawa T, Namikawa H (February 2020). "Cephalodiscus planitectus sp. nov. (Hemichordata: Pterobranchia) from Sagami Bay, Japan". Zoological Science. 37 (1): 79–90. doi:10.2108/zs190010. PMID 32068377. Retrieved 2020-09-17.


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