The order Zoantharia Rafinesque, 1815 (Cnidaria, Anthozoa: Hexacorallia): supraspecific classification and nomenclature

Abstract Many supraspecific zoantharian names have long and complicated histories. The present list is provided to advise researchers on the current state of supraspecific nomenclature of the zoantharians, particularly given the recent attention paid to the taxonomy, phylogeny, and biodiversity of this order. At the same time, several taxonomic issues brought to light by recent research are resolved. Details on the taxonomic and nomenclatural history of most groups are provided, along with appendices of invalid supraspecific names.


Introduction
The Zoantharia are an order of Hexacorallia most closely related to the sea anemones (Actiniaria) (Kayal et al. 2013). They are found in most marine ecosystems. Despite their cosmopolitan distribution and high frequency in many ecosystems, compared to both Actiniaria and Scleractinia, research on this order has been relatively scant. This is due to both their high levels of intraspecific morphological variation (e.g. Burnett et al. 1997, Reimer et al. 2004, Ong et al. 2013 and the presence of incrustations in their body walls (for all zoantharian families except the Zoanthidae), which makes internal histological examination problematic . Taxonomic identification problems have been compounded by a general lack of utility in some traditionally used diagnostic characters (Sinniger et al. 2010a, Swain 2010. Thus, despite being common in many ecosystems (Karlson 1980), until very recently zoantharian taxonomy has been confused (Burnett et al. 1997).
However, recent molecular phylogenetic examination of zoantharians, combined with a reassessment of their taxonomy and diagnostic characters, has led to the group becoming somewhat ordered (Reimer et al. 2007a, 2008a, Sinniger et al. 2010a, 2013, 2013, Swain and Swain 2014Swain et al. 2015), setting an example for the reorganization of other anthozoan groups. This follows in the footsteps of the database Biogeoinformatics of Hexacorallia (Fautin and Buddemeier 2008), which was established as a repository for taxonomic and nomenclatural information on the Hexacorallia (see also Fautin 2016).
There is also a bioinformatics rationale for the compilation of such a taxonomic listing. As electronic name-lists of available and valid names become increasingly accessible, the need to link such lists with nomenclators of names will become an imperative. To this end, listings such as the present one can provide clear linkages between valid names and the huge mass of historical names (most of which are synonyms and some being potentially valid), which will effectively reduce the historical 'synonymy load ' (Low and Reimer 2012a: 83) and provide a clear list of available supraspecific names of Zoantharia for future researchers.

Additional notes for introductory text
All valid taxa are treated in the systematics section, with the taxon (genus and species) listed. Synonyms are also listed. Justification for these synonymies is given in the sections that follow (Appendices 1-3). We use the general term "zoantharian" to refer to species within this order, unless when quoting original text in which another term (usually "zoanthid") was used.

Statistics
A total of 16 family-group names are treated. Nine are considered to be valid, six are synonyms, and one is not referable to the order Zoantharia. A total of 102 names at the genus rank are treated. Of these, 28 names are considered to be valid, 38 to be synonyms, 19 are incorrect spellings, 18 are not referable to the order Zoantharia, and two-Stephanidium Hertwig, 1888, and Triga Gray, 1867-are of uncertain placement and validity (see Table 1).

Gender. Feminine.
Diagnosis. Colonial brachycnemic zoantharians with sand/detritus incrustation in the ectoderm and mesoglea. Currently, all species except for two described are zooxanthellate .
Remarks. Specimens examined with a sphincter muscle of linear mesogleal type (Swain et al. 2015).
Although at least 272 species-group names have been established in the genera Palythoa and Protopalythoa in the literature (see Fautin and Buddemeier 2008), with more research, these species-group names will likely be found to be synonyms-the result of high level of intraspecific morphological variation (see Burnett et al. 1994, Reimer et al. 2006, Hibino et al. 2014.
Remarks. Species of the genus Zoanthus and Acrozoanthus have a double sphincter muscle, which is unique among zoantharians. Referred to in Swain et al. (2015) as discontiguous mesogleal type.
Despite over 150 species having been described in or assigned to this genus (see Fautin and Buddemeier 2008), many of the species-group names are likely to be synonyms-due to the high level of intraspecific morphological variation (see Burnett et al. 1995, 1997, Reimer et al. 2004. One species, Zoanthus praelongus Carlgren, 1954, has recumbent (non-erect) polyps (as in the genus Isaurus) but is clearly referable to Zoanthus (see Carlgren 1954, Reimer et al. 2008b).
The genus Acrozoanthus has a long and complicated taxonomic history. Reimer et al. (2011b) discussed that "despite its very similar appearance, Acrozoanthus australiae was placed into a genus separate from Zoanthus due to the presence of an axial skeleton (Saville-Kent 1893). Later it was shown that this skeleton was in fact a result of habitat preference as Acrozoanthus inhabits the outside of eunicid worm tubes, and the genus was subsequently merged back again into the genus Zoanthus (Haddon 1895). Subsequent to its original description, this species was not mentioned in literature again until its rediscovery by Ryland (1997), based on examination of a single specimen. Further work by Ryland and co-workers described the nematocysts of Acrozoanthus australiae  and also an unusual 'budding' method of asexual reproduction (Ryland 1997), which was theorized to potentially confirm the placement of this species in its own genus".
Molecular phylogenetic data indicate that Acrozoanthus is within the Zoanthus (see Reimer et al. 2011b) monophyly. However, due to a need for more detailed investigations, we refrain from synonymising Acrozoanthus with Zoanthus.

Type species. Isaurus tuberculatus
Remarks. Specimens examined with an orthogonally-reticulate mesogleal sphincter muscle (Swain et al. 2015). Ryland and Lancaster (2003) recognised only three valid species in this genus, although 22 species have been described in or assigned to this genus.
As discussed in Sinniger and Häussermann (2009: 26), this genus is characterised by the "[p]olyps usually strongly encrusted with sand particles. Species found on rocky substrata or gastropod shells often inhabited by pagurids; some cases of free-living species reported (E. lindhali, E. vagus). In colonial species, polyps linked by stolons or, in pagurid-associated species, by a continuous coenenchyme. No symbioses with Symbiodinium zooxanthellae".
Remarks. This genus is monospecific, and is comprised of the type species Paleozoanthus reticulatus, which has not been encountered since it was first described. Due to similarities in sphincter muscles (Swain et al. 2015) further studies are needed to determine if this genus corresponds to Terrazoanthus.

Thoracactis Gravier, 1918
Thoracactis : 12. Thoracactus Walsh, 1967  Remarks. This is a monospecific genus comprised of only the type species Thoracactis topsenti. In describing Thoracactis topsenti,  incorrectly identified it as an actinian (anemone) based on the lack of zooxanthellae, channels, gaps, or cell islets. Although currently placed in the family Epizoanthidae, based on the current understanding of the type species, this genus is referable to the family Parazoanthidae, although an examination of the type material will be necessary to confirm this (see Reimer et al. 2010a: 158).

Terrazoanthus Reimer and Fujii, 2010
Terrazoanthus Reimer and Fujii, 2010: 20. Type species. Terrazoanthus onoi Reimer and Fujii, 2010, by original designation. Gender. Masculine. Diagnosis. This genus is characterised by being a member of the Hydrozoanthidae that is found on rocky substrates (as opposed to being obligate symbionts with hydrozoans). Some species in this genus are also brightly coloured (see Reimer and Fujii 2010: 20).

Nanozoanthidae Fujii and Reimer, 2013
Nanozoanthidae Fujii and Reimer, 2013: 512. Type genus. Nanozoanthus Fujii and Reimer, 2013. Diagnosis. "Well developed polyps connected by narrow stolon. Mineral particles encrusted in column from aboral end to the edge of the oral disc. Irregularly sized sand particles encrusted into ectoderm and slightly into mesoglea. Zig-zagged, white-colored pattern following outside edge of oral disc. Macrocnemic mesenterial arrangement. Sphincter muscle mesogleal. No lacunae or ring sinus. Zooxanthellate. Mitochondrial cytochrome oxidase subunit I and 16S ribosomal DNA sequences significantly differ from all other known zoanthid genera (Fig. 1, 2)." .
Remarks. A monogeneric family. Molecular data position this family in an intermediate position between the Brachycnemina and Macrocnemina, although currently it is placed within Macrocnemina .
Gender. Masculine. Diagnosis. As for family above.
Remarks. This is a monospecific genus currently, with specimens reported from southern Japan, Western Australia, and the Red Sea ). However, molecular data indicate that the European species Isozoanthus sulcatus (Gosse, 1859) likely also belongs to this genus .

Parazoanthus
Remarks. "The original morphological description of Parazoanthus mentions several characteristics such as diffuse endodermal sphincter, encircling sinus, endodermal canals, lacunae and cell-islets in the mesoglea, continuous ectoderm and bodywall incrusted with mineral particles, often with numerous sponge spicules present in the incrustations. As shown in Sinniger et al. (2005) and here, these morphological characteristics alone do not ascertain the monophyly of Parazoanthus. Morphological characteristics in zoanthids can often become artifactual due to both complications encountered in making thin cuttings of heavily sediment incrusted polyps, and in interpreting the results of such sections. In the past, the large majority of epizoic macrocnemic zoanthids were described as belonging to Parazoanthus despite clearly different ecologies in many cases.
Thus, the results of this study strongly suggest that only zoanthid species able to associate with sponges should remain in Parazoanthus, as the type species of this genus, P. axinellae from the Mediterranean Sea, is regularly associated with demosponges." (Sinniger et al. 2010a: 69).
There is a need for a new diagnosis of this genus-grouping. With the recent erection of Umimayanthus Montenegro, Sinniger and Reimer, 2015 and the resurrection of Bergia Duchassaing de Fonbressin and Michelotti, 1860 in Montenegro et al. (2015a), the genus Parazoanthus now consists only of the former phylogenetic grouping of Parazoanthus 'clade C' sensu Sinniger et al. (2010a) and is monophyletic (Montenegro et al. 2015a: 71). Parazoanthus can be distinguished from Bergia and Umimayanthus by 16S-rDNA sequences, lacking the unique 60 bp deletion of Bergia and the unique insertion and deletion of Umimayanthus. Thus, the molecular characters described in Sinniger et al. (2008Sinniger et al. ( , 2013 appear to be efficient in identifying to genus level and could be used as diagnostic characters.
Gender. Masculine. Diagnosis. Sinniger et al. (2010a: 63) originally diagnosed this genus as a group that "grows exclusively on antipatharians" and lacking skeletal secretion.
Remarks. No mesogleal canals or sinus, encrustation to outer mesoglea (Swain and Swain 2014), examined species with either branchiform endodermal or endomeso transitional sphincter muscle (Swain et al. 2015). Sinniger et al. (2010a: 63) discussed that "[t]he type species A. macaronesicus was originally included in the description of Savalia (Gerardia) macaronesica (Ocaña and Brito 2003), and later the description was amended and the authors suggested the possible placement of this species in a separate genus (Ocaña et al. 2007). The species name was accorded to the genus gender. Skeletal secretion (similar to Savalia spp.) was advanced by Ocaña and Brito (2003) as occurring in Antipathozoanthus macaronesicus, and this remains to be studied in detail in order to assess whether this is an isolated characteristic or if it is taxonomically informative at genus level." It also appears at least one member of this genus can be found on gorgonian octocorals (Bo et al. 2012).
Gender. Feminine. Diagnosis. "… can be distinguished from all other zoantharians including Parazoanthus spp., Umimayanthus spp. and Epizoanthus spp. by a unique deletion of 60 bp (from position 133 to 192 in our alignment) and several consecutive base substitutions in the 16S-rDNA region. These characters clearly separate this genus from all other genera inside the family Parazoanthidae, as well as from the genus Epizoanthus" (Montenegro et al. 2015a: 68).
Remarks. Long considered to be a junior subjective synonym of Parazoanthus Haddon and Shackelton, 1891, recent molecular and morphological work by Montenegro et al. (2015a) have shown that the type species, Bergia catenularis Duchassaing de Fonbressin and Michelotti, 1860, represents a generic-level monophyly and resurrected the genus-group name Bergia Duchassaing de Fonbressin and Michelotti, 1860, for this grouping.
This genus-grouping currently contains three species all found in the Atlantic Ocean, although there is evidence of undescribed species in the Pacific Ocean (Montenegro et al. 2015a: 68).
Examined species in this genus-grouping have either branchiform endodermal or simplified mesogleal sphincter muscles (Swain et al. 2015).
Remarks. Monospecific deep-sea genus, appears to be specifically epibiotic on paragorgiid octocorals, and described from and only reported from the Hawaiian Archipelago, although likely present throughout the Pacific .
Remarks. A monospecific genus thus far only reported from the Ryukyu Islands, Japan.
Remarks. Currently this deep-sea genus includes only one species, known from a few locations in the Hawaiian Archipelago ).
The status of this genus is currently very confused. With the utility of the characters of the sphincter muscle in zoantharians in question (see Swain 2010, Sinniger et al. 2010a, it is clear that more research is needed to clarify the diagnosis and taxonomic position of Isozoanthus. The taxonomy is further complicated by the recently described species (the hydroid-associated Hydrozoanthus antumbrosus (Swain, 2009) originally described within Isozoanthus), and the octocoral-associated Isozoanthus primonodius Carreiro-Silva, Braga-Henriques, Sampaio, de Matos, Porteiro and Ocaña, 2010) clearly belong to other genera based on ecology and morphology. Furthermore, only limited molecular data is available for the type species Isozoanthus giganteus. Data in Swain (2010) indicate that Isozoanthus giganteus is highly divergent from both the well-researched species of Isozoanthus-Isozoanthus sulcatus (Gosse, 1859)-and all known zoantharians. Recent work by Fujii and Reimer (2013) shows that I. sulcatus is likely within the Nanazoanthidae Fujii and Reimer, 2013. However, as additional information on Isozoanthus giganteus is lacking, the diagnosis is retained with the caveat that any assignment of species to this genus should include: 1) phylogenetic confirmation of a close relationship with Isozoanthus giganteus; and 2) the elimination of any possibility that the species in question does not belong to another parazoanthid genera based on morphology, ecological associations, and/or habitat.
Remarks. Currently this genus comprises only one species, which was reported as parasitic on Kulamanana haumeaae.
Gender. Feminine. Diagnosis. Macrocnemic genus associated with octocorals and secreting a golden to dark brown scleroproteic skeleton. Ectoderm absent of mineral particles, with well-developed coenenchyme completely covering the host. Characteristic insertion/deletion pattern in the 16S V5 region sensu Sinniger et al. (2005)  .
Remarks. The type species has been reported to live primarily on isidid corals (bamboo corals) (Sinniger et al. 2013: 6). Reported from the Hawaiian Archipelago, Line and Jarvis Islands, Palmyra Atoll, Kingman Reef, all in the Pacific .

Type species. Mesozoanthus fossii
Gender. Masculine. Diagnosis. "Macrocnemic with Parazoanthus-like growth-form. Well-developed polyps with long and pointed tentacles; polyps form clusters linked by a basal coenenchyme. DNA sequences significantly differ from those in other genera..." and "In contrast to Parazoanthus, members of Mesozoanthus usually occur in small patches and are not known to colonise demosponges. No symbioses with Symbiodinium zooxanthellae." (Sinniger and Häussermann 2009: 32).
Gender. Masculine. Diagnosis. No mesogleal canal system in the column. Secreting a black or dark brown horny skeleton, azooxanthellate.
Remarks. Examined species in this genus-grouping have branchiform endodermal or cyclical transitional sphincter muscle (Swain et al. 2015). Distinction from the other skeleton-secreting zoantharians such as Kulamanamana or potentially Antipathozoanthus can be made through habitat (shallow vs. deep-sea) and/or molecular signatures.
There has been historical and recent controversy over the correct name for this genus-group, and this is discussed in detail in Appendix 3.
Gender. Masculine. Diagnosis. "…can be distinguished from all zoantharians including Parazoanthus spp. by a highly conservative and unique insertion of 9 bp in length (from position 556 to 564 in alignment) and one deletion of 14 bp long (from position 574 to 587) in the mt 16S-rDNA region" (Montenegro et al. 2015b: 76).
Remarks. Specimens examined from this genus-grouping have a branchiform endodermal sphincter muscle (Swain et al. 2015).
"…exclusively associated with sponges, usually encrusting and cushion sponges, occasionally with massive sponges. Polyps generally scattered over the sponge surface, but can form defined stoloniferous chains in lines, or form groups of two to three connected polyps. Polyps may be solitary or connected to each other by a stolon through a thin but clearly visible coenenchyme either over or under the sponge surface. Polyps with sand particles and detritus incrusted in column. Tentacles equal or longer than the expanded oral disc diameter." (Montenegro et al. 2015b: 76).
This genus-group currently includes four described species; three in the Indo-Pacific and one in the Atlantic (Montenegro et al. 2015b).

Type species. Zibrowius ammophilus
Gender. Masculine. Diagnosis. "Sand incrusted, arborescent fan shaped colonies, golden skeleton, well developed coenenchyme completely covering the host, can be confused with Kulamanamana, but easily distinguished by the presence of sand incrustation in the ectoderm, characteristic insertion/deletion pattern in the 16S V5 region" sensu Sinniger et al. [2005] (Sinniger et al. 2013: 7) Remarks. Until now, only reported from the Cross Seamount in the central Pacific Ocean.

Suborder incerta sedis
Remarks. Two families are currently not assigned to any suborder.
Remarks. A monogeneric family. Molecular data places this family in an unresolved position distant from the Brachycnemina and Macrocnemina.
Diagnosis. Very small (diameter 1.5-2.2 mm, height 1 mm), unitary polyps, with microcnemes and macrocnemes, although their arrangement could not be clearly seen. Mesenteriel insertions make body wall to have a furrowed appearance, with spherical evaginations on the body wall above the area where the sphincter muscle is present. Twenty-six mesenteries.
Remarks. From the original description, possibly a species of zoantharian, but type material needs to be located and examined. We make no decision as to the validity of this genus and species in the event that the identification of this genus and species requires a reversal of precedence Article 23. 9 (ICZN 1999: 27, 28) with a later (but more widely-used name). Also, the genus-group name Stephanidium Hertwig, 1888, is preoccupied by Stephanidium Ehrenberg, 1839 (incerta sedis).

Discussion
As can be seen from examining the nomenclatural and taxonomic history of the various supraspecific names in this paper, many taxa of the order Zoantharia have a confused history. However, over the past two decades, phylogenetic and detailed morphological examinations of zoantharians have resulted in a new understanding of the evolutionary relationships within the order , Reimer et al. 2007a, 2008a, Sinniger et al. 2010a, 2013, 2013Swain et al. 2015). Combined with a recent effort to organize the nomenclature of zoantharians (Low and Reimer 2011aReimer , b, 2012a, it can be said that much of the Zoantharia nomenclature is now stable, and generally reflects our current understanding of their evolutionary history. However, as seen in this manuscript, there are still some nomenclatural issues that remain to be resolved. For example, the validity of the genera Sphenopus and Acrozoanthus still have to be thoroughly examined. Furthermore, it is clear from recent molecular phylogenetic results ) that the taxonomy and nomenclature of the suborders are in urgent need of a revision. Finally, at the ordinal level, it appears that Zoantharia is much closer to the Actiniaria (sea anemones) than has been previously thought . As these two orders have been speculated to be basal cnidarians (Kayal et al. 2013), after clarification of their evolutionary history, subsequent nomenclatural amendment may be needed.
Additional work examining the utility of ecological and morphological traits of Zoantharia as diagnostic characters is needed to allow the linkage of current phylogenetic results with past literature (Swain et al. 2016). Despite, or perhaps due to its confused and challenging morphological taxonomy, the order Zoantharia is now among the most advanced hexacorallian order in terms of the use of molecular tools to clarify phylogenetic relationships between taxa at various taxonomic levels. As such, and despite potential and known differences in molecular evolution of other anthozoans (Stampar et al. 2014), Zoantharia is a potentially good model for clarifying the taxonomy of other hexacorallian orders and anthozoan groups.
Monaco) for providing literature. Siong-Kiat Tan (National University of Singapore) provided comments on nomenclatural issues. Sung-yin Yang (University of the Ryukyus, Japan) helped getting references. Saulo Bambi and Cecilia Volpi of the Museo di Storia Naturale Università di Firenze (sez. Zoologica "La Specola"), Italy, are thanked for their assistance in locating and photographing the syntype of Gemmaria rusei Duchassaing de Fonbressin and Michelotti, 1860. Ray B. Williams (Tring, United Kingdom) provided information on the works of Angelo Andres and Philip Henry Gosse. Neal L. Evenhuis (Bishop Museum, Honolulu, Hawaii) provided copies of literature and provided comments on many of the dates of publications of the works cited. Daphne G. Fautin (University of Kansas) generously shared her bibliography (now published as Fautin 2016) of the Cnidaria (from the database "Hexacorallians of the World") with us and her discussions with the first author through the years have greatly improved the content of this work. Peter K. L. Ng (National University of Singapore) has also provided guidance and advice on nomenclatural matters through the years. Helmut Zibrowius provided us with a tremeduous amount of old literature on Zoantharia. Comments from Marymegan Daly (Ohio State University) and an anonymous reviewer on an earlier manuscript (that now forms part of Appendix 3) greatly improved the information presented therein. This work was sponsored in part by the International Research Hub Project for Climate Change and Coral Reef/Island Dynamics at the University of the Ryukyus, as well as by a JSPS Kiban B grant entitled "Global evolution of Brachycnemina and their Symbiodinium" and by a Japan Society for the Promotion of Science (JSPS) 'Zuno-Junkan' grant entitled "Studies on origin and maintenance of marine biodiversity and systematic conservation planning" to the senior author.

Appendix 2.
Nomenclator of genus-group names in the Zoantharia Rafinesque, 1815 Names in bold and designated with an asterisk (*) are considered to be valid genusgroup names. In accordance with Article 67.2 of the Code (ICZN 1999: 66, 67), all type species designations made herein are from among the "originally included nominal species". Names marked with a † are invalid synonyms, or incorrect spellings (if further denoted by a " [sic]"). Additional names without either designation have been confused with the order Zoantharia at one time or another but have since been removed from this group. The identity of two possible zoantharian genus-group name-Stephanidium Hertwig, 1888, and Triga Gray, 1867-will need to be resolved. Reimer and Fujiwara, in Reimer, Sinniger, Fujiwara, Hirano and Maruyama, 2007: 258 [sic]. Incorrect spelling of Gerardia Lacaze-Duthiers, 1864, by H. Schmidt (1972: 452 fig. 3) based on an unnamed cnidarian described and illustrated by Hughes (1750: 293, 294, pl. 24, fig. 1) that is clearly not a zoantharian (see also Ryland and Lancaster 2003: 411;Fautin 2016: 182). Actinia calendula Ellis, in Ellis and Solander, 1786, is currently considered to be assigned to the genus Petalactis Andres, 1883(see Fautin 2016, thereby making Hughea Lamouroux, 1821, a synonym of Petalactis Andres, 1883. Also see the unnecessary replacement name Meto Gistel, 1848. Hughuea [sic]. Incorrect spelling of Hughea Lamouroux, 1821, by Gistel (1848.
As discussed by Low and Reimer (2012b), the name Palythoa savignyi was proposed by Audouin (1826: 229) for an unnamed figured by Savigny (1811: pl. 2, fig.  1) from Egypt. Based on the figure and the other information provided by Savigny (1811) and Audouin (1826), we herein agree with the opinion of Ehrenberg (1834a: 269; 1834b: 45) in considering Palythoa savignyi Audouin, 1826, to be a valid species of zoantharian, but unlike this previous author, we consider it to be a species of Palythoa Lamouroux, 1816. As the type species of the genus Palythoaster Haeckel, 1875, is considered to be a species of Palythoa Lamouroux, 1816, the former becomes a junior subjective synonym of the latter. of Mammillifera nymphaea Le Sueur, 1817. From the synonymy of "Polythoa (Mammithoa) nymphosa Dana", it is clear that the species-group name "nymphosa Dana" was a replacement for nymphaea Le Sueur, 1817. Although the species-group name nymphosa was attributed to Dana (see also Walsh 1967: 28), this species-group name was never used by Dana, and the authorship of Polythoa (Mammithoa) nymphosa should be attributed to Andres (1883a: 534, 535), and the name is herein considered an unnecessary replacement name for (and objective synonym of ) Mammillifera nymphaea Le Sueur, 1817.
It was probably for these reasons that Haddon and Shackleton (1891a: 626) designated Gemmaria rusei Duchassaing de Fonbressin and Michelotti, 1860, as the type species of Gemmaria Duchassaing de Fonbressin and Michelotti, 1860. The spelling of the type species, Gemmaria rusei Duchassaing de Fonbressin and Michelotti, 1860, requires some discussion. The International Commission on Zoological Nomenclature (ICZN 1998: 121, 122) ruled that the spellings of two genus-and species-group names derived from the surname Riise but earlier incorrectly spelled as Rüsei by Duchassaing de Fonbressin and Michelotti (see Bayer and Grasshoff 1997: 11) should be corrected. However, Gemmaria rusei Duchassaing de Fonbressin and Michelotti, 1860, was not one of the names that was ruled on. The spelling of the type species of Gemmaria Duchassaing de Fonbressin and Michelotti, 1860, should thus remain as Gemmaria rusei Duchassaing de Fonbressin and Michelotti, 1860 (but see also Ryland and Lancester 2003: 410 [i]f an author publishes a new genus-group name expressly as a new replacement name (nomen novum) for a previously established name … both the prior nominal taxon and its replacement have the same type species, and type fixation for either applies also to the other, despite any statement to the contrary".
Although the specific identity of Gemmaria rusei Duchassaing de Fonbressin and Michelotti, 1860, will require further research, we herein assign this species-group taxon to Palythoa Lamouroux, 1816. Protopalythoa Verrill, 1900, thus becomes a junior subjective synonym of Palythoa Lamouroux, 1816. Likewise, the preoccupied genusgroup name Gemmaria Duchassaing de Fonbressin and Michelotti, 1860, as well as Parapalythoa Verrill, 1900 (discussed below), and Haplotella Stechow, 1919 (also discussed below), become junior subjective synonyms of Palythoa Lamouroux, 1816. Verrill (1900: 562, 1907 himself had already observed the close affinity between Protopalythoa Verrill, 1900, andPalythoa Lamouroux, 1816, stating "[t]he name Gemmaria having been preoccupied in Hydrozoa, it is necessary to give a new one to this group, if it is to be considered as really distinct from Palythoa, from which it seems to differ only in the fact that the zoöids are not united together laterally by coenenchyma, but only by stolons or based expansions. Some species of Palythoa are not thus united for more than half their height, or even less, and perhaps future discoveries may show a complete gradation between the two conditions" (Verrill 1900: 562). Similarly, Verrill (1907: 287) also discussed that: "[s]hould they [i.e., the species assigned to Protopalythoa] ultimately prove to be identical, it would probably be necessary to unite the genus Protopalythoa (= Gemmaria of many authors) to Palythoa … The only tangible difference between the two genera is the presence in the latter of a thick crust-like coenenchyma, uniting the polyps together laterally. But in this species they are often united for less than half their height".
Two other genus-group names need to be discussed. Parapalythoa Verrill, 1900, is another genus-group name that needs to be discussed in connection with Gemmaria Duchassaing de Fonbressin andMichelotti, 1860. Verrill (1900: 560) proposed the name Parapalythoa for specimens of "Gemmaria Rusei" described by McMurrich (1889: 124, 125) from Bermuda. Verrill (1900: 560) considered the material studied by McMurrich (1889) to be distinct from Gemmaria rusei Duchassaing de Fonbressin and Michelotti, 1860, and proposed that they should be called Parapalythoa heilprini. Although Verrill (1907: 283) later stated that the genus-group name Parapalythoa was an error for Protopalythoa, this statement has no bearing on the availability of the genus-group name Parapalythoa, and the name remains an available one, with Parapalythoa heilprini Verrill, 1900, being the type species by monotypy. Regardless of the validity of Parapalythoa heilprini Verrill, 1900, it is clear that Verrill (1900: 560) was intending to establish a new genus-group for a taxon similar to, but distinct from, Gemmaria rusei Duchassaing de Fonbressin and Michelotti, 1860. As discussed above, Gemmaria rusei Duchassaing de Fonbressin and Michelotti, 1860, is herein considered to be a species of Palythoa Lamouroux, 1816, and as the differences in the specimens of "Gemmaria rusei" described by McMurrich (1889: 124, 125) not being sufficient for a distinction at the genus-group level, we herein consider Parapalythoa Verrill, 1900, to also be a junior subjective synonym of Palythoa Lamouroux, 1816. A final name that needs to be discussed in connection with Gemmaria Duchassaing de Fonbressin and Michelotti, 1860, is Haplotella Stechow, 1919. Stechow (1919 proposed the name Haplotella as a replacement name for Gemmaria Duchassaing de Fonbressin and Michelotti, 1860, and has the same type species (see discussion above). Haplotella Stechow, 1919, is a junior objective synonym of Gemmaria Duchassaing de Fonbressin and Michelotti, 1860, and a junior subjective synonym of Protopalythoa Verrill, 1900, andParapalythoa Verrill, 1900. The date of publication of Haplotella is conventionally cited as "1920", but in an abstract to the work that appeared in 1919, the following was stated: "Die Aktiniengattung "Gemmaria" Duchassaing et Michelotti 1861 erhält wegen Präokkupation durch ein Hydroidengenus den Namen Haplotella" (Stechow, 1919: 853). The date of publication of the name Haplotella is thus 1919.
In conclusion, the genus-group names Gemmaria Duchassaing de Fonbressin and Michelotti, 1860, Parapalythoa Verrill, 1900, Protopalythoa Verrill, 1900, and Haplotella Stechow, 1919, are all herein considered to be synonyms of Palythoa Lamouroux, 1816. Furthermore, the genus-group name Protopalythoa Verrill, 1900, can no longer be used by authors who consider Gemmaria variabilis Duerden, 1898 (and other related species) to be be sufficiently distinct to require a genus-group of its own (i.e. Protopalythoa sensu Ryland and Lancaster 2003). To resolve this, a new genus-group name will need to be established. a family-group name is evidenced by their use of "Zoanthidae" (containing "Zoanthus", "Isaura", "Mammillifera" and "Orinia n. g.") as a counterpart to "Polythoae". The name "Polythoa" is an incorrect subsequent spelling of Palythoa Lamouroux, 1816 (the first usage of which appears to be by Schweigger 1819: 100).
To prevent the nomenclatural and taxonomic destabilisation that would result from the replacement of Sphenopidae Hertwig, 1882, with its subjective synonym Palythoidae Duchassaing de Fonbressin and Michelotti, 1860, as required by the Principle of Priority (Article 23, ICZN 1999: 24) requires that the oldest available name for the taxon under consideration must be used.
To mediate the Principle of Priority, Article 23.9.1 of the Code (ICZN 1999: 27) allows for a reversal of precedence of a junior synonym when the senior synonym has not been used as a valid name after 1899 (Article 23.9.1.1) and the junior synonym "has been used for a particular taxon, as its presumed valid name, in at least 25 works, published by at least 10 authors in the immediately preceding 50 years and encompassing a span of not less than 10 years" (Article 23.9.1.2).
Since 1899, the name Palythoidae has been used in three publications. The first usage was by Barel and Kramers (1977: 32) used the term "species of Palythoidae" for an unidentified zoantharian associated with echinoderms. From the context, it appears that Barel and Kramers (1977: 32) were reporting on material with close affinities to Palythoa Lamouroux, 1816.
As Ng & Low (2010:37, 38) have argued, "valid usage" of a name must be unambiguous and show clearly that the author[s] both considered it the correct name to be used and adopted the name. According to these criteria, the usage of "Palythoidae" by Barel and Kramers (1977: 32) cannot be considered to be valid.
The third usage is by Pax and Müller (1957: 3, 4) in which they recognise the "Unterfamilie Palythoinae" under Epizoanthidae, and further provide a key for identifying this subfamily. Clearly, Pax and Müller (1957: 3, 4) were recognising the family-group name Palythoidae as vaild.
The name Palythoidae Duchassaing de Fonbressin and Michelotti, 1860, thus has been used as the valid name for the taxon is denotes since 1899 (and Article 23.9.1.1 of the Code cannot be fulfulled). Table 1. An updated supraspecific classification of the Zoantharia. All valid genera and their type species are given. The numbers given in parentheses after each suborder and family represent the total number of families and genera, respectively, in each grouping. A total of one order, three suborders, nine families and twenty-seven genera are currently recognised in the Zoantharia.