Parachrysogorgia octagonos ( Versluys, 1902 ) Xu & Zhan & Xu, 2023

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, Zootaxa 5321 (1), pp. 1-107 : 36-40

Parachrysogorgia octagonos ( Versluys, 1902) comb. nov.

Figs. 17–20

Chrysogorgia octagonos Versluys, 1902: 65–67 , figs. 99–103.

Chrysogorgia octagonos: Kükenthal 1919: 525 .

Material examined. MBM286860 , station FX-Dive 216 (10°5′47″N, 140°11′20″E), a seamount (tentatively named as M5) on the Caroline Ridge, 975 m, 4 June 2019 .

Description. Specimen bottlebrush-shaped and attached to a rocky substrate, about 24 cm long and 5 cm wide in maximum with an oval white holdfast about 1.5 cm in diameter ( Fig. 17A, B ). Stem about 2 mm in diameter at base and brown with a little aeruginous metallic luster. Branching sequence 1/4R. Branches subdivided dichotomously, up to five orders with branching angle 60°–80°. Distance between adjacent branch 2–3 mm, orthostiche intervals 10–12 mm, the first internode of branch about 4–7 mm and the terminal branchlets up to 15 mm. Polyps 2–3 mm tall, and 1–2 mm wide, some of them up to 3 mm wide with an expanded body ( Fig. 17D, E ). Polyps usually absent on first and second internode, and arranged one to three in terminal branchlets ( Fig. 17C ). Eight blunt and warty points present beneath the tentacles ( Fig. 17D, E ). Small zooids without obvious polyp oral disc and tentacles, 0.15–0.75 mm tall, cylindrical and occasionally warty, numerous in number, densely arranged on the surface of stem and the first internodes ( Fig. 20A, B ). Scales in zooids longitudinally or obliquely arranged, elongate and smooth, usually biscuit-shaped with a slightly medial contraction and toothed edges, some of them lobed with irregular outline, measuring 85–190 × 33–58 μm ( Fig. 20C–E ).

Rods and plates in the basal tentacle rachis longitudinally arranged and usually in two rows, thick and irregular with more lobed edges, smooth, some of them with many large warts or ridges on surface, usually one end thick and the other end flat and broad, measuring 231–598 × 48–288 μm ( Figs. 17D , 19C ). Scales in the upper part of tentacle rachis small and curved, nearly smooth and almost with fine toothed edges and a medial contraction, some of them lobed and twisted with irregular edges and shapes, occasionally with sparse fine warts, measuring 68–234 × 13–95 μm ( Fig. 19B ). Scales in pinnules longitudinally arranged, slender and smooth, often a little curved and twisted, measuring 98–262 × 14–54 μm ( Fig. 19D ). Scales in the upper part of polyp body wall thick and smooth with lobed edges and various shape, some of them curved and sharp at one or two ends, broad and lobed at the other end, combining to form a warty and blunt point at the base of a naked tract below each tentacle, measuring 227–827 × 29–308 μm ( Figs. 17D , 19A ). Scales in basal part of polyp body wall longitudinally and transversely arranged, elongate and smooth with a slight medial contraction, some of them with finely toothed edges and lobed with an irregular outline, measuring 112–613 × 37–263 μm ( Fig. 18A ). Scales in coenenchyme arranged along to the branch, elongate and smooth, usually lobed with irregular edges and a slight medial contraction, some of them branched with various shape, measuring 125–550 × 25–156 μm ( Fig. 18B ).

Distribution and habitat. Timor Sea, 520 m ( Versluys 1902); a seamount on the Caroline Ridge, 975 m.

Remarks. Our specimen of P. octagonos ( Versluys, 1902) matches well with the original description. This species has a bare, sclerite-free area present at the base of the tentacle and is classified to the genus Parachrysogorgia . It is most similar to P. expansa ( Wright & Studer, 1889) , and according to the description of Versluys (1902), they may be the same species with intraspecific variation, which needs to be confirmed further. At present, based on the known morphological features, P. octagonos can be separated from P. expansa by its relatively flat and smooth sclerites at the tentacle base (vs. thick and often with many large warts on surface) and more projecting and curved points at the base of tentacular part (vs. a little projecting and blunt) ( Wright & Studer 1889, Versluys 1902).

Genus Chrysogorgia Duchassaing & Michelotti, 1864

Diagnosis (redefined on the basis of Xu et al. 2020a). Colony branching usually sympodial, occasionally monopodial with a long straight or zigzagging stem, arising from a single ascending spiral (clockwise or counterclockwise, bottlebrush-shaped colony), a fan (planar colony), two or more fans emerging from a short main stem (bi- or multi-flabellate colony), or branches producing on the top of a long unbranched stem (tree-shaped colony). Axis with a metallic shine, dark to golden in color. Branch subdivided dichotomously or pinnately. Most polyps relatively large to the size of the branches they sit on, few in number and well separated from one another. Tentacle rachis arising from the polyp body wall continuously with sclerites not forming a bare, sclerite-free area at the base of tentacle and projections beneath the tentacles. Sclerites in the form of spindles, rods, scales.

Type species. Chrysogorgia desbonni Duchassaing & Michelotti, 1864 , by monotypy.

Distribution. Worldwide in a depth range of 10–4492 m ( Watling et al. 2011)

Figures

FIGURE 17. The external morphology and polyps of Parachrysogorgia octagonos (Versluys, 1902) comb. nov. A, B. The same specimen in situ and after collection. C. A part of branch under a light microscope. D, E. A single terminal polyp under SEM and a light microscope, respectively. Scale bars: 5 cm (B); 5 mm (C); 1 mm (D, E).

FIGURE 18. Sclerites of Parachrysogorgia octagonos (Versluys, 1902) comb. nov. A. Sclerites in the basal part of polyp body wall. B. Sclerites in coenenchyme. Scale bars: 500 μm (A and B in the same scale).

FIGURE 19. Sclerites of Parachrysogorgia octagonos (Versluys, 1902) comb. nov. A. Sclerites on the upper part of polyp body wall. B. Sclerites on the upper part of tentacle rachis. C Sclerites on the basal part of tentacle rachis. D. Sclerites in pinnules. Scale bars: 500 μm (A, C in the same scale); 100 μm (B, D in the same scale).

FIGURE 20. The external morphology and sclerites of small zooids. A. A part of branch covered with numerous small zooids. B, C. A single zooid under a light microscope and SEM. D. Two small zooids under SEM. E. Sclerites of the zooid. Scale bars: 2 mm (A), 200 μm (B–D); 100 μm (E).