Rhabdopleurida is one of three orders in the class

Pterobranchia Pterobranchia, members of which are often called pterobranchs, 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 w ...

, which are small, worm-shaped animals, and the only surviving

graptolites Graptolites are a group of colonial animals, members of the subclass Graptolithina within the class Pterobranchia. These filter-feeding organisms are known chiefly from fossils found from the Middle Cambrian (Miaolingian, Wuliuan) through th ...

. Members belong to the

hemichordates Hemichordata ( ) is a phylum which consists of triploblastic, eucoelomate, 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 ...

, colonial, connected with a stolon, living in clear water and

secrete 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 mec ...

tubes called tubarium. They have a single

gonad A gonad, sex gland, or reproductive gland is a Heterocrine gland, mixed gland and sex organ that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gon ...

, the gill slits are absent and the collar has two tentaculated arms. ''Rhabdopleura'' is the best studied pterobranch in developmental biology.

Taxonomy

This small order is

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

. It has only a single extant

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

, containing four to six living species. Order Rhabdopleurida Fowler, 1892 * Family Rhabdopleuridae Harmer, 1905 ** Genus ''Rhabdopleura'' Allman, 1869 *** '' Rhabdopleura annulata'' Norman, 1921 — Indo-Pacific region *** '' Rhabdopleura compacta'' Hincks, 1880 — Atlantic *** '' Rhabdopleura normani'' Allmann, 1869 — Atlantic and parts of the Pacific *** '' Rhabdopleura recondita'' Beli, Cameron and Piraino, 2018 — Mediterranean *** '' Rhabdopleura striata'' Schepotieff, 1909 — Indo-Pacific (

Sri Lanka Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka, also known historically as Ceylon, is an island country in South Asia. It lies in the Indian Ocean, southwest of the Bay of Bengal, separated from the Indian subcontinent, ...

) ''

Nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium,'' it may be impossible to determine whether a ...

'': * '' Rhabdopleura grimaldi'' Julien, 1890 * '' Rhabdopleura manubialis'' Jullien & Calvet, 1903 Extinct species: * †''

Rhabdopleura delmari ''Rhabdopleura'' is a genus of colonial sessility (motility), sessile hemichordates belonging to the Pterobranchia class. They are exclusively marine, benthic organisms whose species occur within all major oceans and range in habitat from intert ...

'' Mortelmans 1955 * †'' Rhabdopleura graysoni'' Chapman, Durman & Rickards, 1995 * †'' Rhabdopleura hollandi'' Rickards, Chapman & Temple, 1984 * †'' Rhabdopleura kozlowskii'' Kulicki, 1969 * †'' Rhabdopleura obuti'' Durman & Sennikov, 1993 * †'' Rhabdopleura sinica'' Chapman, Durman & Rickards, 1995 * †'' Rhabdopleura vistulae'' Kozlowski, 1956

References

Marinespecies.org

ITIS.gov
* Hayward, P.J.; Ryland, J.S. (Ed.) (1990). The marine fauna of the British Isles and North-West Europe: 1. Introduction and protozoans to arthropods. Clarendon Press: Oxford, UK. . 627 pp. Hemichordates Bilaterian orders {{hemichordate-stub