A new genus and species of golden coral (Anthozoa, Octocorallia, Chrysogorgiidae) from the Northwest Atlantic

Abstract A new genus and species of unbranched golden coral, Flagelligorgia gracilis, is described based on several specimens collected off the southeastern coast of the United States. The genus is provisionally included in the family Chrysogorgiidae, pending molecular confirmation. Flagelligorgia morphologically resembles other unbranched chrysogorgiids, such as Distichogorgia, Chalcogorgia, Helicogorgia and Radicipes, to which it is compared. The type species is illustrated and its distribution mapped.


Introduction
Chrysogorgiids form a polyphyletic family of octocorals (Pante et al. 2012), which is distributed in all oceans throughout the world ). Most of its genera are in need of revision, some of which require reallocation into new families (Pante et al. 2012). In the course of doing a revision of the genus Radicipes Stearns, 1883 (see Cordeiro et al. in press), an unusual species was encountered that was similar to species in that genus that were already known, but was consistently different from them in several characters. Although no recently collected specimens were available for molecular analysis, sufficient alcohol-preserved specimens were present at the NMNH to describe the new species and the new genus in which it is placed.

Material and methods
All specimens are preserved in ethanol (70%) and deposited at the National Museum of Natural History. Reference material of all species of Radicipes was also examined (Cordeiro et al. in press). The terminology used in the description follows that of Bayer et al. (1983). Preparation of polyps for SEM to reveal sclerites includes short digestion (four seconds) of superficial coenenchyme, rinsing several times in distilled water, and drying at room temperature.
Abbreviations used in the text include: Alb -USFWS Albatross, L:W -length to width ratio of a sclerite, MCC -Monophyletic Chrysogorgiidae Clade sensu Pante et al. (2012), NMNH -National Museum of Natural History, Smithsonian Institution, USNM -United States National Museum (now known as the NMNH, but acronym still used for catalog numbers).  Cairns (2001) and Pante et al. (2012)). Calcaxonians having an unjointed, solid (non-spicular), concentrically layered scleroproteinous axis. The axial layers are usually smooth (not undulated) and thus not longitudinally grooved externally; the axis usually displays metallic or iridescent reflections. The colony may be branched or unbranched (flagelliform), arising from a root-like or discoidal, strongly calcified holdfast. Polyps are contractile but not retractile, arranged in rows (uniserial, biserial or multiserial), but never in whorls. Sclerites predominantly flat, smooth scales, in some species warty rods and spindles.

Subclass
Remarks. Fourteen genera have been assigned to the Chrysogorgiidae, but based on sequencing of three genes, Pante et al. (2012) have suggested that only six of these genera belong to Chrysogorgiidae sensu stricto, which they call the Monophyletic Chrysogorgiidae Clade, or MCC. They imply that the other genera may belong to as many as three other, as yet undescribed, families. The six genera of the MCC are keyed by Pante and France (2010) and their worldwide distributions plotted by Watling et al. (2011). They are further discussed by Pante et al. (2012) in the context of a phylogenetic analysis. Flagelligorgia is morphologically most similar to Radicipes, which is part of the MCC, but lacking material suitable for molecular analysis, the placement of Flagelligorgia in that family can only be a suggestion at this time. In fact, we did attempt to sequence four genes (COI, mtMutS, 28S and 18S) from specimens collected in 1964 with no results.
Distribution. Worldwide, 31-4492 m depths (Pante and Watling 2011: 6). Remarks. Until 1956 (Bayer 1956) the Chrysogorgiidae had been divided into three subfamilies, one being the Lepidogorgiinae Versluys, 1902, consisting of genera with an unbranched colony and lacking polyp opercula. However, the subfamily classification has been ignored for decades and is not supported by molecular evidence. Nonetheless, it is incumbent to compare Flagelligorgia to the four other unbranched chrysogorgiid genera. Helicogorgia Bayer, 1981, known only from the east coast of Africa at 66-775 m depth range, is unbranched but has its polyps arranged in a multiserial fashion on one side of the stem, a naked track displayed on the opposite side. Furthermore, its body wall scales are irregular plates and its coenenchymal scales are spindles. For all of these reasons Helicogorgia is easily distinguished from Flagelligorgia. Based on sequencing of three genes, Pante et al. (2012) indicate that Helicogorgia might constitute a family on its own, as sister to the Chrysogorgiidae. Helicogorgia was revised by Williams (1992), recognizing four species in the African coast.
Chalcogorgia Bayer, 1949, known only from its type locality off northwestern Cuba at 708 m depth, is also unbranched and has biserially arranged polyps, like Flagelligorgia, but differs in having eight triangular opercular scales on each polyp, and body wall scales shaped as irregularly shaped platelets. According to Pante et al. (2012: 8), based on "very limited data," Chalcogorgia was suggested to ally with Helicogorgia, and thus also outside of the MCC.
Distichogorgia Bayer, 1979, known only from the Blake Plateau off Florida at 814 m depth, is unbranched and has biserially arranged polyps, but differs in having unique body wall scales consisting of two fans of longitudinally arranged, blade-like scales, one on each side of the polyp, interspersed with tiny pointed sclerites, similar to its coenenchymals. Pante et al. (2012) did not report sequencing data for this genus, but based on its biserially polyps, they suggested an affinity with Helicogorgia and Chalcogorgia in a family separate from the Chrysogorgiidae.
Perhaps most similar to Flagelligorgia is the genus Radicipes Stearns, 1883, consisting of 9-10 species (see Cordeiro et al., in press), which occurs worldwide at depths of 241-3580 m. Radicipes is unbranched but differs from Flagelligorgia in having uniserially arranged polyps, and a body wall and coenenchymal sclerites that are rod-shaped to compressed rod-shaped. Furthermore, chrysogorgiids (MCC), including Radicipes, are characterized by having an axis formed by non-undulated (smooth) concentric layers (Bayer 1956), which is not the case for Flagelligorgia. Based on molecular evidence Pante et al. (2012) placed Radicipes firmly in the Chrysogorgiidae clade (MCC), as the sister genus to Chrysogorgia. Lacking molecular evidence for Flagelligorgia (all specimens are quite old), it is not possible at this time to determine if it is allied with Radicipes in the Chrysogorgiidae (based on similarity of body wall sclerites) or the other cluster of genera including Helicogorgia, Chalcogorgia and Distichogorgia (based on polyp arrangement), which may constitute an as yet undescribed family.
Distribution. Off Southeastern United States from North Carolina to Florida, 196-567 m depths.
Etymology. Named gracilis (Latin for slender, gracile), in allusion to the very slender aspect of the colony.