Description
All known species live in a secreted coenecium attached to a rock substrate. 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. ''Cephalodiscus'' zooids are also more mobile than their ''Rhabdopleura'' counterparts, and are able to move around within tubarium, 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.Species
19 living species of ''Cephalodiscus'' have been described: * ''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''.Historical discovery
''Cephalodiscius'' are Endemism, endemic to the Antarctic and Southern Ocean, whose relative inaccessibility has historically limited human study of the genus. The Ross expedition, ''Erebus'' and ''Terror'' may have unwittingly encountered ''C. nigrescens'' specimens, and the HMS Challenger, ''Challenger'' ''C. densus''; but until the Swedish Antarctic Expedition of 1901-1903, only ''C. dodecalphus'' had been identified. In 1882, M'Intosh (later spelled McIntosh) had identified ''Dodecalphus'' from Dredging, dredged Magellanic Straits, Magellanic-Straits material, work published 5 years later, but the discovery left cephalodiscid phylogeny unclear. 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. ''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.References
External links
* * Cephalodiscus, Hemichordate genera Pterobranchia {{hemichordate-stub