Chrysogorgia acanthella ( Wright & Studer, 1889 ) Versluys, 1902

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 : 76-83

Chrysogorgia acanthella ( Wright & Studer, 1889) Versluys, 1902

Figs. 48–51 ; Tables 8 , 9

Dasygorgia acanthella Wright & Studer, 1889: 18–20 , Pl. IV, fig. 6; Pl. V, fig. 8.

Chrysogorgia acanthella: Versluys, 1902: 71–73 , fig. 113.

Chrysogorgia acanthella: Kükenthal, 1919: 526 .

Chrysogorgia acanthella: Pasternak, 1981: 50–51 .

Material examined. MBM286862 , station FX-Dive 211 (10°2′57″N, 140°10′29″E), a seamount (tentatively named as M5) on the Caroline Ridge, 1478m, 29 May 2019 . MBM286357 , station FX-Dive 70 (11°16′14″N, 139°25′30″E), a seamount (tentatively named as M2) near the Mariana Trench, 1458 m, 27 March 2016 .

Description. Colonies bushy bottlebrush-shaped in situ and attached to a rocky substrate ( Figs. 48A , 50A ). Specimen of MBM286862 about 23 cm long and 14 cm wide in maximum with the holdfast not recovered ( Fig. 48B ). Stem about 2.5 mm in diameter at base with a little aeruginous metallic luster. Branching sequence 2/5L, 3/7L and irregular on the top. Branches subdivided dichotomously, up to 10 orders with branching angle 60°–80°. Distance between adjacent branch 3–19 mm, the first internode of branch 9–25 mm long and the terminal branchlets gracile and up to 22 mm long. Polyps usually with an oval body and became narrow at tentacle base, 1–2 mm tall and 1.0– 1.5 mm wide, occasionally up to 3 mm in terminal ( Fig. 48C–E ). Polyps arranged two to four and often small on first internode, one to four in medial internode and up to five in terminal branchlets. Polyps in stem internodes very small and arranged two to eight in each internode. Eggs often observed in the bulbous base of polyps ( Figs. 48C , 50C ). Verrucae occasionally present on the polyp body ( Fig. 50C ).

Scales in aboral face of tentacle rachis usually alternately arranged in two rows with irregular shape, nearly smooth and a little curved with one or two ends became broad, some of them with sparse fine warts, measuring 50– 387 × 11–147 μm ( Fig. 49A ). Scales in pinnules longitudinally arranged, slender and a little curved, nearly smooth or with sparse fine warts, some of them with one end became broad and the other end narrow or sharp, measuring 61–253 × 7–107 μm ( Fig. 49C ). Scales at the base of tentacular part obliquely or transversely arranged, elongate and nearly smooth with irregular shape, usually with an obvious medial contraction, some of them with finely toothed edge surface and one end truncated and the other rounded, measuring 87–333 × 27–153 μm ( Fig. 49E ).

Scales in basal part of polyp body wall obliquely or transversely arranged, elongate and nearly smooth with an obvious medial contraction, relatively regular with biscuit-like shape, occasionally with lobed and finely toothed edges, measuring 84–513 × 23–229 μm ( Fig. 49B ). Scales in coenenchyme arranged along to the branch, small, a little elongate and smooth with a slight medial contraction, occasionally lobed with irregular shape, measuring 67–297 × 20–83 μm ( Figs. 48F , 49D ). Rods and plates or scales in polyp mouth area small and thick, nearly smooth or coarse with deep cracks or sparse warts on surface, some of them with a medial contraction, measuring 24–83 × 4–28 μm ( Fig. 49F ).

Specimen of MBM286357 bushy with possible 1/3L branching sequence on the basal part and became more irregular on the upper part. Polyps on branch internodes pitcher-shaped, usually with eight inconspicuous tentacles gathering on the top ( Fig. 50C–E ). Polyps in stem internodes small and arranged average three in each internode. Spindles and scales in polyp mouth area near the tentacles thick with many coarse warts on surface, some of them curved and with irregular edges ( Fig. 51D ). The morphological measurements of MBM286357 see the Table 3 .

Distribution and habitat. North of the Kermadec Islands, 1097 m ( Wright & Studer 1889); Marcus-Necker Ridge, 1700–2300 m ( Pasternak 1981); a seamount near the Mariana Trench, 1458 m; a seamount on the Caroline Ridge, 1478 m.

Remarks. Our specimens MBM286862 and MBM286357 differ from the holotype by more irregular branching sequence (2/5L, 3/7L and irregular in top vs. possible 1/3L and irregular in top vs. 2/5L), longer interbranch distance (3–19 mm vs. 12–15 mm vs. 1.5 mm). These differences may be caused by different growth stage or environment, and are not constant, we treat as the intraspecific variation. Therefore, the characters of C. acanthella can be summarized by having a bushy bottlebrush-shaped colony, usually pitcher-like polyps, irregular scales with one or two ends broad in tentacle rachis, biscuit-like scales in basal part of polyp body wall, elongate scales with a slight medial contraction in coenenchyme.

Figures

FIGURE 48.The external morphology andpolyps of Chrysogorgia acanthella (Wright & Studer,1889), specimen MBM286862. A, B. The same specimen in situ and after collection. C, D. Single non-terminal polyps under a light microscope and SEM, respectively. E. A single terminal polyps under SEM. F. A part of branch under SEM. Scale bars: 10 cm (B); 1 mm (C–E); 300 μm (F).

FIGURE 49. The sclerites of Chrysogorgia acanthella (Wright & Studer, 1889), specimen MBM286862. A. Sclerites in tentacle rachis. B. Sclerites in polyp body wall. C. Sclerites in pinnules. D. Sclerites in coenenchyme. E. Sclerites at the base of tentacular part. F. Sclerites in polyp mouth area. Scale bars: 300 μm (A–E in the same scale); 50 μm (F).

FIGURE 50.The external morphology andpolyps of Chrysogorgia acanthella (Wright & Studer,1889), specimen MBM286357. A, B. The same specimen in situ and after collection. C–E. Non-terminal polyps with eggs in bulbous base under a light microscope and SEM, respectively. F. A part of branch under SEM. Scale bars: 10 cm (B); 1 mm (C–E); 200 μm (F).

FIGURE 51. Sclerites of Chrysogorgia acanthella (Wright & Studer, 1889), specimen MBM286357. A. Sclerites in tentacle rachis. B. Sclerites in polyp body wall. C. Sclerites in coenenchyme. D. Some warty sclerites in polyp mouth area near the tentacles. E. Sclerites in pinnules. Scale bars: 300 μm (A–C in the same scale); 100 μm (D, E in the same scale).