''Rhabdopleura'' is a

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 ...

of colonial sessile

hemichordate 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 incl ...

s belonging to the

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 ...

class. They are exclusively marine, benthic organisms whose species occur within all major oceans and range in habitat from intertidal to c. 900 m.Gordon, D.P., Quek, Z.B.R., Orr, R.J.S. et al. (2023). Morphological diversity and a ribosomal phylogeny of Rhabdopleura (Hemichordata: Graptolithina) from the Western Pacific (Singapore and New Zealand), with implications for a re-evaluation of rhabdopleurid species diversity. Mar. Biodivers. 53, 4 (2023). https://doi.org/10.1007/s12526-022-01310-3 As one of the oldest living genera with a fossil record dating back to the

Middle Cambrian Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek (di ...

, it is also considered to be the only living

graptolite 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 t ...

s. ''Rhabdopleura'' is the best studied pterobranch in

developmental biology Developmental biology is the study of the process by which animals and plants grow and develop. Developmental biology also encompasses the biology of Regeneration (biology), regeneration, asexual reproduction, metamorphosis, and the growth and di ...

. Research in the 2010s by Jörg Maletz and other paleontologists and biologists have demonstrated that ''Rhabdopleura'' is an extant

History

The first evidence for extant species of ''Rhabdopleura'' ('' Rhabdopleura normani'') was identified in the Shetland Islands in 1869. Since then, a total of at least nine extant species have been identified.WoRMS Editorial Board (2025). “Rhabdopleura Allman, 1869”. World Register of Marine Species. https://www.marinespecies.org/aphia.php?p=taxdetails&id=137594

Species

List of species from WoRMS Editorial Board (2025): ;Living species The genus ''Rhabdopleura'' contains at least nine living species. * '' Rhabdopleura annulata'' Norman 1921 — Indo-Pacific region * ''Rhabdopleura chathamica'' Gordon, Quek & Huang 2024Gordon, D.P., Quek, Z.B.R., Huang, D. (2024). “Four new species and a ribosomal phylogeny of Rhabdopleura (Hemichordata: Graptolithina) from New Zealand, with a review and key to all described extant taxa”. ''Zootaxa''. 5424(3):323-357. http://dx.doi.org/10.11646/zootaxa.5424.3.3 — South Pacific * '' Rhabdopleura compacta'' Hincks 1880 — Atlantic * ''Rhabdopleura decipula'' Gordon, Quek & Huang 2024 — South Pacific * ''Rhabdopleura emancipata'' Gordon, Quek & Huang 2024 — South Pacif * ''Rhabdopleura francesca'' Gordon, Quek & Huang 2024 — South Pacific * '' Rhabdopleura normani'' Allmann, 1869 — Atlantic and parts of the Pacific * '' Rhabdopleura recondita'' Beli, Cameron and Piraino, 2018 — Mediterranean * '' Rhabdopleura striata'' Schepotieff 1909 — 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, ...

) ; ;''

Nomina dubia 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 ...

'' (doubtful) * '' Rhabdopleura grimaldi'' Julien 1890 nomen dubium * '' Rhabdopleura manubialis'' Jullien & Calvet 1903 nomen dubium ;Extinct species * †'' Rhabdopleura delmari'' 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

Morphology

Individual ''Rhabdopleura'' larvae are lecithotrophic with planula-like features and a uniform arrangement of cilia. Those larva metamorphosize into individual zooids with a bilaterally symmetrical body plan and a single pair of tentacled arms used in feeding. The zooid body is tripartite, being divided into a protostoma, a mesostoma and a metastoma. Generally speaking, the zooids appear to remain integrated with the larger stolon systems of their colonies throughout their lives.

Colonies

''Rhabdopleura'' colonies are thought to begin when an individual larva secretes an initial dome structure known as a prosiculum. Inside the prosiculum, the individual larva then metamorphosizes into a foundational

zooid A zooid or zoöid is an animal that is part of a colonial animal. This lifestyle has been adopted by animals from separate unrelated taxa. Zooids are multicellular; their structure is similar to that of other solitary animals. The zooids can ...

. This zooid emerges from the prosiculum and proceeds to secrete an initial tube. From within this tube, an individual bud forms that produces a second zooid. The second zooid may then produce its own tube, along with a corresponding bud.Beli E, De Castro Mendonça LM, Piraino S, Cameron CB. (2022). “Development and Phenotypic Plasticity of Tubes and Tubaria of the Living Graptolite Rhabdopleura recondita (Pterobranchia, Hemichordata)”. ''Diversity''. 14(12), 1080. https://doi.org/10.3390/d14121080 The collective aggregation of tubes within the colony is known as a coenicium and the zooids that inhabit it are themselves connected to one another via living tissue referred to as stalks or stolon.Brusca, R. C. (2023). ''Invertebrates'' (W. (Entomologist) Moore & G. Giribet (Eds.); Fourth edition.). Oxford University Press. Although most species of ''Rhabdopleura'' appear to form the prosiculum directly within the water column, one species, '' Rhabdopleura recondita,'' is known to form colonies inside the calcareous skeletons of dead

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic animal, aquatic invertebrate animals, nearly all living in sedentary Colony (biology), colonies. Typically about long, they have a spe ...

n colonies.

Feeding

Like other pterobranchs, ''Rhabdopleura'' are considered ciliary mucus suspension feeders that predominantly consume either suspended particles and/or diatoms. While feeding, individual zooids from a colony project their arms out from openings in the coenicium and proceed to remove particulate matter from the water column.

Fossil record

The

fossil record A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

for ''Rhabdopleura'' dates back to the

. There are also ''Rhabdopleura'' fossils from the

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

.A.J. Chapman; P.N. Durman; R.B. Rickards. 1995
Rhabdopleura hemichordates: new fossil forms and review
''Proceedings of the Geologists' Association'' Volume 106, Issue 4, 1995, Pages 293-303.

References

{{Taxonbar, from=Q2808627 Hemichordate genera Extant Cambrian first appearances