World List of Octocorallia
This World List of Octocorallia is part of the World Register of Marine Species (WoRMS), a global initiative to provide an online register of scientific names of all marine organisms. In this continuously updated list, users can find the current taxonomic classification of octocorals, with valid and invalid names of taxa, their distributions, literature and historical citations.
Origin
This list started as a contribution to UNESCO-IOC Register of Marine Organisms by L.P. van Ofwegen, S.D. Cairns & J. van der Land (eds) (2000-2007). Originally maintained by L.P. van Ofwegen as a list of valid octocoral species, since 2019 it has been revised and updated to include all valid and invalid names of taxa with links to original descriptions and other taxonomic literature.
Introduction
Octocorals (Cnidaria: Anthozoa: Octocorallia) constitute a diverse group of about 3500 species of corals commonly known as soft corals, gorgonians, sea fans, sea whips and sea pens. Members of Class Octocorallia are distinguished from other anthozoan corals (Class Hexacorallia) by their eight-part symmetry, reflected in the number of tentacles (8) and internal mesenteries of the polyps. The number of tentacles is invariant within the Class and the tentacles are almost always pinnate (i.e., having side projections, resembling feathers). With a single known exception, all octocorals are colonial organisms whereby every individual is made up of many interconnected feeding polyps. Octocorals may or may not have a skeleton. Gorgonians (sea fans, sea whips) are octocorals that have internal skeletal axes composed of calcium carbonate and/or the horn-like protein gorgonin. Those octocorals referred to as soft corals or stoloniferans lack a skeletal axis but typically have free calcitic skeletal elements (sclerites) embedded in their tissues. Sea pens are morphologically specialized for life in soft sediments, with a bulbous base (peduncle) that serves as an anchor, and polyps arranged around a distal rachis that is usually supported by an internal rod of calcium carbonate. Blue corals, Heliopora spp., are true reef-building octocorals that produce a massive skeleton of aragonitic calcium carbonate similar to that of the scleractinian corals. Octocorals are exclusively marine but can be found in all marine environments from the intertidal to depths of 4000 m and from the poles to the tropics. They are most diverse in deep waters (>50 m) (Cairns 2007) where they form three-dimensional marine animal forests and coral gardens that support a high diversity of other organisms. They are also diverse in shallow-water tropical reef environments, where phase shifts to octocoral-dominated communities are increasing in frequency with climate change (Lasker et al. 2020; Reverter et al. 2021).
Systematics
Throughout most of the 20th century, octocorals were classified based on the overall colony growth form, including the presence (or not) of a skeletal axis and the composition of that axis (calcitic vs. proteinaceous). The morphologically distinctive sea pens and blue coral were separated into orders Pennatulacea and Helioporacea respectively, with all other octocorals included in a single order, Alcyonacea (Bayer 1981). Order Alcyonacea was further divided among as many as six subordinal groups including Calcaxonia (gorgonians with a solid calcareous axis); Holaxonia (gorgonians with a largely proteinaceous axis); Scleraxonia (gorgonians with an axis of consolidated or fused sclerites); Alcyoniina (soft corals, lacking an axis but with polyps embedded in a mass of tissue); Stolonifera (forms lacking an axis but with polyps connected by simple stolons or membranes); and Protoalcyonaria (the sole species with a solitary growth form). The recognition of transitional forms whose morphology spanned suborders suggested that these groups might not represent clades (Bayer 1981). Indeed, the first molecular phylogenetic studies of octocorals confirmed that few if any of these subordinal groups or orders were monophyletic (Berntson et al. 2001;McFadden et al. 2006, 2010). Attempts to further resolve the ordinal- and family-level phylogeny of octocorals using single-locus genetic markers were, however, largely unsuccessful (McFadden et al. 2022). As a consequence, for two decades the taxonomy remained unrevised despite widespread recognition that Bayer’s (1981) classification scheme did not reflect the phylogenetic relationships within the class.
Phylogenomic analyses based on hundreds to thousands of nuclear genes have now largely resolved the relationships among families, and the entire class has recently been revised (McFadden et al. 2022). Octocorallia is currently recognized to include two reciprocally monophyletic orders, Scleralcyonacea and Malacalcyonacea. Scleralcyonacea (“hard alcyonaceans”) includes the sea pens (superfamily Pennatuloidea), blue corals (family Helioporidae), and many deep-water taxa of gorgonians (former Calcaxonia and Scleraxonia). Malacalcyonacea (“soft alcyonaceans”) includes the majority of shallow-water soft corals and stoloniferans (taxa lacking an axis) as well as gorgonians with largely proteinaceous axes (former Holaxonia) and some former Scleraxonia. There are, however, no clear synapomorphies defining either of these orders and (with the exception of sea pens and blue corals) it is difficult to predict to which order a species belongs based on gross colony morphology alone (McFadden et al. 2022). A number of genera for which molecular data are not yet available remain incertae sedis (unclassified) at the family level as their morphology does not allow us to predict their ordinal or familial affiliation.
Species Identification
While phylogenomic approaches have allowed better understanding of the higher order taxonomic relationships of Octocorallia, identification of species remains extremely challenging. Most genera are greatly in need of revision, many species remain undescribed and the number of valid species remains unknown. Species are discriminated largely on the basis of differences in the shape, size and anatomical distribution of sclerites (microscopic calcitic skeletal elements) in the tissues that are difficult to quantify or assess objectively, and there are few practicing taxonomists with the necessary expertise. Most original species descriptions published before the late 20th c. are inadequately or too sparsely illustrated to allow species to be identified with certainty. Redescription of original type material using modern imaging technologies such as scanning electron microscopy will be necessary to revise taxonomy and provide reliable identification resources. Until such resources become available, it will remain impossible to identify taxa to the species level in most genera.
Citation
Usage of data from the World List of Octocorallia in scientific publications should be acknowledged by citing as follows:- McFadden, C.S.; Cordeiro, R.; Samimi-Namin, K.; Williams, G.; van Ofwegen, L. (2025). World List of Octocorallia. Accessed at https://www.marinespecies.org/octocorallia on 2025-06-08. doi:10.14284/749
Individual pages are individually authored and dated. These can be cited separately: the proper citation is provided at the bottom of each page.
Feedback
The authors welcome input from users of this website who detect errors or omissions: we strive to maintain the website as both a comprehensive and an up-to-date resource and acknowledge that it is still a work in progress. We aim to update the database regularly and frequently.
The taxonomy in the World List of Octocorallia is edited and updated by volunteer experts, assisted by the Data Management Team (DMT) at VLIZ. Authors are encouraged to send copies of publications to the respective editor or the DMT with details of new or revised nomenclature.
Other Useful Resources
Bayer FM (1981) Key to the genera of Octocorallia exclusive of Pennatulacea (Coelenterata: Anthozoa), with diagnoses of new taxa. Proc. Biol. Soc. Wash. 94: 902-947.
Bayer FM, Grasshoff M, Verseveldt J (1983) Illustrated trilingual glossary of morphological and anatomical terms applied to Octocorallia. EJ Brill / Dr. W. Backhuys, Leiden.
Coral Trait Database, https://www.coraltraits.org/
Fabricius K, Alderslade P (2001) Soft corals and sea fans: a comprehensive guide to the tropical shallow-water genera of the Central West-Pacific, the Indian Ocean and the Red Sea. Australian Institute of Marine Science, Townsville. [available as a pdf at https://www.researchgate.net/figure/Fabricius-KE-Alderslade-P-2001-Soft-Corals-and-Sea-Fans-A-comprehensive-guide-to-the_fig1_258516656 ]
McFadden CS, van Ofwegen LP, Quattrini AM (2022) Revisionary systematics of Octocorallia (Cnidaria: Anthozoa) guided by phylogenomics. Bull. Soc. Syst. Biol. 1(3): 8375.
Williams GC (1995) Living genera of sea pens (Coelenterata: Octocorallia: Pennatulacea): illustrated key and synopses. Zool. J. Linn. Soc. 113: 93-140.
Image credits: C.S. McFadden
