Chrysogorgia cylindrata Xu & Zhan & Xu 2023, sp. nov.

Chrysogorgia cylindrata sp. nov. Figs 21–33; Tables 8, 9 urn:lsid:zoobank.org:act: 67E52CEA-4937-4DF4-96A9-5DA442601058 Material examined. Holotype: MBM286463, station FX-Dive 221 (10°3′12″N, 140°9′43″E), a seamount (tentatively named as M5) on the Caroline Ridge, 1877 m, 9 June 2019. Paratypes: MBM286355, station FXDive 61 (11°21′10″N, 139°20′29″E), a seamount (tentatively named as M2) near the Mariana Trench, 907 m, 18 March 2016. MBM286460, station FX-Dive 210 (10°4′39″N, 140°12′7″E), M5 seamount, 936 m, 28 May 2019. MBM286461, station FX-Dive 210 (10°4′N, 140°12′E), M5 seamount, 870–944 m, 28 May 2019. MBM286462, station FX-Dive 216 (10°5′26″N, 140°11′12″E), M5 seamount, 907 m, 4 June 2019. MBM286464, station FX-Dive 215 (10°4′49″N, 140°10′54″E), M5 seamount, 901 m, 2 June 2019. Diagnosis. Chrysogorgia with a long cylindrical and bottlebrush-shaped colony in adults and a discoidal holdfast. Branching sequence 2/ 5L. Polyps usually 1–2 mm long, arranged up to four in branch internodes. Scales in tentacle rachis usually thick and slender, nearly smooth or with sparse fine warts, branched or forked with irregular shape. Scales in pinnules slender, nearly smooth or with sparse fine warts, some of them forked or narrow in ends. Scales in polyp body wall elongate and nearly smooth with a medial contraction, some of them irregular edges. Scales in coenenchyme slender and smooth, usually with lobed and irregular edges. Spindles and elongate plates or scales in polyp mouth area near the tentacles thick with many obvious warts, often curved with irregular shape. Description. Holotype long cylindrical and bottlebrush-shaped with main stem a little curved, about 42 cm long and 7 cm wide in maximum with the holdfast not recovered (Fig. 21B). Stem about 1.5 mm in diameter at base, brown with aeruginous metallic luster. Branching sequence 2/ 5L. Branches subdivided dichotomously, up to five orders with branching angle 90°–100°. Distance between adjacent branch 2–5 mm, orthostiche intervals 12–30 mm, the first internode of branch about 13 mm and the terminal branchlets up to 11 mm. Polyps 1–2 mm tall, average 1.5 mm, some of them up to 3.5 mm in terminal, and about 1 mm wide with eight obvious extended tentacles. Terminal polyps cylindrical (Fig. 21D, G) and non-terminal polyps usually with an expanded oval body (Fig. 21C, E, F). Polyps usually arranged two to four on first internode, one and rarely two in medial internodes and one or two in terminal branchlets. Polyps in stem 0.5–1.0 mm tall, arranged two to four on each internode. Tentacular part about 1 mm long, some of them up to 2 mm with tentacles extended. Verrucae absent. Scales in aboral face of tentacle rachis transversely arranged, some of them obliquely or longitudinally at base, slender and a little curved, usually branched or forked with irregular shape and lobed edges, thick and nearly smooth or with sparse fine warts and occasional long ridges on surface, measuring 137–400 × 17–233 μm (Fig. 22B). Scales in pinnules longitudinally arranged, slender with sparse fine warts, some of them nearly smooth and a little curved with one end forked or became narrow, measuring 128–364 × 10–130 μm (Fig. 22E). Scales in polyp body wall longitudinally or transversely arranged, stacked with each other, elongate with an obvious medial contraction and irregular and often lobed edges, some of them with deep marginal lobes forming various shape, measuring 111–401 × 21–227 μm (Fig. 22A). They nearly smooth with edge surface slightly shallow toothed, some of them with sparse fine warts. Scales in coenenchyme arranged along to the branch, slender and smooth, often with irregular edges, occasionally with sparse fine warts, measuring 80–360 × 14–107 μm (Figs. 21H, 22D). Spindles and elongate plates or scales in polyp mouth area near the tentacles thick with many obvious conical or large warts, often curved with irregular shape, some of them forked in one end, measuring 214–343 × 15–96 μm (Fig. 22C). Sclerites same in terminal and non-terminal polyps. Variation of paratypes. For the morphological measurements of paratypes, see Table 3. The paratype specimens have different external colony: MBM286461 with the smallest size about 6 cm long, MBM286460 and MBM286462 with a small bottlebrush-shaped colony about 20 cm and 16 cm long, respectively. MBM286463 and MBM286355 with a long cylindrical colony as same as the holotype, about 42 cm and 54 cm long, respectively. Polyps absent on the main stem in MBM286461 while present on the other paratypes and the holotype. Verrucae numerous on the branch and some uncharacterized features (something like Chrysogorgia tricaulis Pante & Watling, 2012) on the back of upper part of tentacle rachis in MBM286460 (Figs. 27, 28), while absent in other specimens. Scales in polyp body wall all elongate, but more regular in MBM286461, relatively regular with fewer lobes in MBM286460 and 286462, irregular with more lobes in the holotype, MBM286355 and 286464. Sclerites in tentacles all irregular in shape, but more slender with relatively sharp ends in MBM286460–286462. Scales in coenenchyme all elongate and smooth, but relatively stout and regular in MBM286461, slender with fewer lobes in MBM286460 and 286462, slender with more lobed edges in the holotype, MBM286355 and 286464. Type locality. A seamount (tentatively named as M5) on the Caroline Ridge with water depth of 1877 m. Etymology. The Latin adjective cylindratus (cylindrical) refers to the cylindrical shape of the colony. Distribution and habitat. Found from the seamounts on the Caroline Ridge and near the Mariana Trench in the Western Pacific Ocean with water depths of 870–1877 m. Colonies attached to a rocky substrate (e.g., Fig. 21A). The water temperatures were 2.46–5.47°C and the salinity 36.16–36.84. ......continued on the next page TABLE 8. (Continued) ......continued on the next page TABLE 9. (Continued) .....continued on the next page TABLE 9. (Continued). * , putative species or questionable regarded by Versluys, 1902. Remarks. The specimens of Chrysogorgia cylindrata all have a bottlebrush-shaped colony, 2/5L branching sequence and the same sclerite form, for example, scales slender and branched with various shape in the back of tentacle rachis, scales elongate with a medial contraction and lobed edges in polyp body wall, scales slender and often lobed with various shape in coenenchyme, and warty and thick sclerites near the polyp mouth area. Moreover, their 28S gene sequences showed they are identical with the intraspecific differences (see the genetic analysis before). Thus, we identified the six specimens as the same species. There are a few morphological variations among them as described before. However, these differences are not constant and may be caused by different growth stages or environment or inadequate measurement, and we thus treat as the conspecific variation. The six specimens of C. cylindrata sp. nov. showed a series of growth stages. Considering the diameter of the stem base and colony size, the specimen MBM286461 is juvenile with a weak bottlebrush-shaped colony, MBM286460 and MBM286462 are in an intermediate state with a short bottlebrush-shaped colony, and MBM286463, MBM286464 and MBM286355 are adult with a long and slender bottlebrush-shaped colony. Furthermore, the sclerite shapes seem to be uniform in the specimens with same growth stage. Chrysogorgia cylindrata sp. nov. belongs to Versluys’ group C, and is characterized by a slender bottlebrush-shaped colony in adults, smooth and slender scales in coenenchyme, elongate scales with a medial contraction and often broad lobed edges in polyp body wall. Chrysogorgia cylindrata sp. nov. are similar to C. acanthella (Wright & Studer, 1889), C. pendula Versluys, 1902 and C. campanula Madsen, 1944 in sclerite forms and branching sequences, but differs from them by more slender scales in coenenchyme (vs. all oval or biscuit-like, relatively stout), more elongate scales in polyp body wall (vs. all relatively stout), longer and more slender colony in adults (bottlebrush-shaped vs. all relatively small bottlebrush-shaped or bushy colony) (Table 9).Published as part of Xu, Yu, Zhan, Zifeng & Xu, Kuidong, 2023, Studies on western Pacific gorgonians (Anthozoa: Octocorallia, Chrysogorgiidae). Part 1: a review of the genus Chrysogorgia, with description of a new genus and three new species, pp. 1-107 in Zootaxa 5321 (1) on pages 40-58, DOI: 10.11646/zootaxa.5321.1.1, http://zenodo.org/record/820341