Cephalodiscida is one of two orders in the class

Pterobranchia Pterobranchia is a class of small worm-shaped animals. They belong to the Hemichordata, and live in secreted tubes on the ocean floor. Pterobranchia feed by filtering plankton out of the water with the help of cilia attached to tentacles. The ...

, which are small, worm-shaped animals. Members belong to the

hemichordates Hemichordata is a phylum which consists of triploblastic, enterocoelomate, and bilaterally symmetrical marine deuterostome animals, generally considered the sister group of the echinoderms. They appear in the Lower or Middle Cambrian and includ ...

. Species in this order are

sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...

, living in clear water and

secrete 440px Secretion is the movement of material from one point to another, such as a secreted chemical substance from a cell or gland. In contrast, excretion is the removal of certain substances or waste products from a cell or organism. The classical ...

tubes on the

ocean floor The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as 'seabeds'. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...

Taxonomy

The order is a small one, with only two known families, each containing a single

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

. The validity of the family Atubaridae, who has only a sole member, is regarded as questionable. * Order Cephalodiscida Fowler 1892 ** Family Cephalodiscidae Harmer 1905 *** Genus †'' Aellograptus'' Obut 1964 *** Genus †'' Eocephalodiscus'' Kozlowski 1938 ex Kozlowski 1949 *** Genus †'' Melanostrophus'' Öpik 1930 ex Öpik 1933 *** Genus †'' Pterobranchites'' Kozlowski 1967 *** Genus '' Atubaria'' Sato 1936 *** Genus ''

Cephalodiscus ''Cephalodiscus'' is a genus of hemichordates in the monotypic family Cephalodiscidae of the order Cephalodiscida. Description Unlike ''Rhabdopleura'', ''Cephalodiscus'' species do not form large colonies and are only pseudocolonial. ''Cephalod ...

'' M'Intosh 1882

References

Harmer. S. F. 1905. The Pterobranchia ol the Siboga-Expedition. Siboga Exped. Monogr. 26. 1-131 Hemichordates Deuterostome orders {{hemichordate-stub