An illustrated key to the genera and subgenera of the Recent azooxanthellate Scleractinia (Cnidaria, Anthozoa), with an attached glossary

Abstract The 120 presently recognized genera and seven subgenera of the azooxanthellate Scleractinia are keyed using gross morphological characters of the corallum. All genera are illustrated with calicular and side views of coralla. All termes used in the key are defined in an illustrated glossary. A table of all species-level keys, both comprehensive and faunistic, is provided covering the last 40 years.


Introduction
The ready identification of azooxanthellate Scleractinia (determined herein by depth of occurrence and previously published observations) to the genus and species levels has been hampered by a lack of a comprehensive key to the genera as well as a lack of species level keys. For instance, the last comprehensive set of keys to the genera was published by Vaughan and Wells (1943) almost 70 years ago, and relied in part on microstructural characters that were both hard to observe (requiring thin sectioning) and interpret.
Since then the number of Recent azooxanthellate genera and species has almost doubled, and new observations on apozooxanthellate species (species that have facultative symbiosis with zooxanthellae) are also available. Furthermore, what keys exist to the species level of various taxa or geographic regions are scattered throughout the literature and of variable quality (Table 1). In this Table, tabular keys are included, as they provide as much if not more information than a conventional dichotomous key. As result of the application of molecular data (e.g. Fukami et al. 2008, Kitahara et al. 2010a, Huang et al. 2011, Stolarski et al. 2011, Arrigoni et al. 2012, the higher taxonomic ranks of the order Scleractinia were shown to be polyphyletic. As such, a key to this taxonomic rank seems premature. Thus, it is the purpose of this paper to provide a single, comprehensive, illustrated key to the presently recognized 120 azooxanthellate scleractinian genera and 7 additional subgenera. We constructed the key using gross morphological characteristics of the corallum, which, when used in conjunction with the glossary and illustrations, we hope will provide a guide to the proper genus identification. But one must keep in mind that this key, as most, will not necessarily supply a definitive identification of the genus, as its use depends on the interpretation of the characters as well as the variation of that character state. We have used many of the dichotomies published by Vaughan and Wells (1943), but avoided the microstructural characters, and updated the taxa. Whereas microstructure is undoubtedly a valuable set of characters to define genera, in most cases it is not necessary to identify the genera. Among the 120 extant azooxanthellate scleractinian genera, 74 are illustrated with its type species (~61%). Within the remaining 46 genera, 20 (~16,6%) have an extinct species as type, represented by a fossil coral. For them and the remaining 26 genera, the illustrated species present very well the most important morphological characters of their respective genus. table 1. Previously published keys to azooxanthellate taxa, divided as comprehensive keys to all taxa with in a monophyletic taxon, and partial (faunistic) keys of species. Taxa listed alphabetically by taxon name. Tabular keys (T) are included.

Methods
Some genera are keyed two or even three times because of the variation within those genera regarding the characters used in the key. In theory, all variations of that genus will be correctly keyed. Although most couplets are dichotomous, some are polychotomous, such as the columella or colony shape, which allows the reader to clearly see the multiple states of a particular character.
Although it would be desirable to follow the generic key with keys to all of the approximately 720 azooxanthellate species, it is a simple fact that not many species level keys have been published. Those that have been published in the last 35 years are listed in Table 1, separated as to whether they are keys to all of the taxa within a monophyletic taxon (comprehensive) or to a more limited fauna of a region (faunistic). Keys made before 1970 were found to be, in general, not up to date and are thus not included. It should be noted that fully one-third of the genera (40) are monotypic, and thus do not require a key following a correct genus identification, and another 22 genera have but two species. Finally, although they do not include keys, the treatises of Wells (1956) and Chevalier and Beauvais (1987) include diagnoses of all genera, including those represented only by extinct species, and thus provide a rich source of taxonomic information.
Other sources of useful taxonomic information include a list of all extant Recent scleractinian species as of 1999 , which also includes a rough indication of their geographic range. The azooxanthellate component of this list is kept up to date as an on-line resource (www.lophelia.org/online-appendices), which now includes junior synonyms and depth ranges of the species, and authors of the genera. A list of the 120 azooxanthellate genera, their authorship, and bathymetric ranges was also published in Roberts et al. (2009:  Geographic ranges within brackets in the key are not meant to be considered as distinguishing characters, but simply informational, which may nonetheless hint at an incorrect identification. Abbreviations: Ant. = Antarctic or Subantarctic, Atl. = Atlantic, IP = Indo Pacific, IWP = Indo-West Pacific, Pac. = Pacific, SubAnt = Subantarctic; Cosmopolitan implies occurrence in all three oceans as well as Subantarctic and/or Antarctic. Museums and Institutions acronyms: AM = Australian Museum (Sydney); AU = Auckland University Museum (Auckland); CSIRO = Commonwealth Scientific and Industrial Research Organisation (Hobart); JCU = James Cook University (Townsville); MNHN = Muséum national d'Histoire naturelle (Paris); SBMNH = Santa Barbara Natural History Museum (Santa Barbara); SIO = Scripps Institute of Oceanography (San Diego); NZOI = New Zealand Oceanographic Institution (now the National Institute of Water and Atmospheric Research) (Wellington); USNM = United States National Museum (now the National Museum of Natural History, Smithsonian) (Washington, D.C.); YPM = Yale Peabody Museum (New Heaven).
Useful sources for more information about definitions of terms used in the glossary include: Wells (1956), and Cairns (1981, 1989.   (Figure 1), usually arranged in hexameral symmetry. Septa are added in cycles, the first cycle composed of 6 septa, the second also of 6, the third of 12, the fourth of 24, the fifth of 48, etc. resulting in corallites consisting of 6, 12, 24, 48, or 96, etc. septa per calice. Septa can bear smooth, dentate, or laciniate axial margin (Figure 1). Solitary Corallum: Solitary coralla exist in a variety of shapes, the shape being one of the criteria used to differentiate genera and species. Many solitary coralla are shaped as an inverted cone (conical), and may be attached and straight or free and usually curved. If the edges of the cone diverge at a hypothetical basal angle of 10-40°, this corallum is called ceratoid (e.g. Plate 10, Figs H-I), if the angle is 40-60°, then trochoid (e.g. Plate 8, Fig. F), if the angle is 60-80°, turbinate (e.g. Plate 13, Fig.  H), and if the angle is 160-180° and the corallum is low, discoidal (e.g. Plate 18, Fig. P). Coralla may also be cylindrical (e.g. Plate 22, Fig. N), and if the cylinder is irregular in shape, scolecoid (e.g. Plate 12, Fig. D). Others are wedge-shaped (cuneiform) or bowl-shaped (e.g. Plate 17, Figs F, H, J, M). Still others have a flat base with a convex upper surface (cupolate) (e.g. Plate 19, Figs A-F) and others are simply onion-shaped or irregular (globular) (e.g. Plate 18, Fig. B). Spongy Columella: See Columella. Stereome: A general term for thick calcareous deposits, generally thickening various parts of the corallum. Stoloniferous Budding: A type of extratentacular budding in which polyps are asexually generated from a thin, elongate, encrusting coenenchymal ribbon, the connecting ribbon often obscured by encrusting organisms (