Chrysogorgia arboriformis, 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 : 59-61

Chrysogorgia arboriformis sp. nov.

Figs. 34–37 ; Tables 8 , 10

urn:lsid:zoobank.org:act:05AC7598-FA40-4FC8-B52B-A4969654961C

Material examined. Holotype: MBM286465 , station FX-Dive 211 (10°2′56″N, 140°10′29″E), a seamount (tentatively named as M5) on the Caroline Ridge, 1482 m, 29 May 2019 . Paratype: MBM286466 , station FX-Dive 225 (10°36′45″N, 140°3′51″E), a seamount (tentatively named as M8) on the Caroline Ridge, 1573 m, 13 June 2019 .

Diagnosis. Chrysogorgia having a tree-shaped colony with a long unbranched stem and a discoidal holdfast. Branching sequence 1/ 3L. Polyps usually with an expanded oval body and became narrow at the base of tentacular part. Scales in tentacle rachis thick and curved with many fine coarse warts, almost branched or forked with irregular shape. Scales in pinnules curved and rib-like, usually with two toothed ends and one serrated side. Scales in polyp body wall nearly smooth with an obvious medial contraction, usually with one or two broad and straight ends in upper part, and some of them lobed with irregular shape in basal part. Scales in coenenchyme slender, nearly smooth or with one or more large warts, some of them irregular with lobed edges.

Description. Holotype tree-shaped with a long unbranched stem, about 45 cm long and 17 cm wide in maximum with the branching part about 15 cm long ( Fig. 34C ). Holdfast white and nearly round, about 2.2 cm long and 1.5 cm wide in maximum. The unbranched part of stem monopodial and a little zigzag at the upper, and have some old scars of the past branches. The branching apart with 1/3L branching sequence and became irregular on the top. Stem about 3.5 mm in diameter at base, brown with aeruginous metallic luster. Branches subdivided dichotomously, up to nine orders with branching angle 60°–80°. Distance between adjacent branch 8–23 mm, orthostiche intervals 26–32 mm, the first internode of branch 8–11 mm and the terminal branchlets up to 23 mm. Polyps 1.0– 2.5 mm tall, average 2 mm, and 1.0– 1.5 mm wide with an expanded oval body and became narrow at the base of tentacular part ( Figs. 34E, F ; 35B–E ). Polyps usually arranged one or two on first internode, sometimes one of them very small, one to six in medial internodes and up to seven in terminal branchlets ( Fig. 35A ). Polyps in stem sparse to rare, often arranged one on each internode. Tentacular part 1.0– 1.5 mm long with eight obvious tentacles. Verrucae absent.

Scales in aboral face of tentacle rachis transversely arranged in a single row, thick, curved and coarse with many fine warts, almost branched or forked with irregular shape, and became small, thin and occasionally longitudinally arranged on the top, measuring 70–349 × 14–251 μm ( Figs. 35F , 36C ). Scales in pinnules longitudinally arranged, slender and curved with rib-like shape and usually two toothed ends and one serrated side, occasionally with a sharp or forked end, nearly smooth in outside surface, some of them with sparse fine warts or large warts on ends, measuring 131–474 × 7–126 μm ( Fig. 36A ). The margins of its two side often bent up to form a shallow groove. Scales in the base of tentacular part longitudinally or transversely arranged, elongate with an obvious medial contraction and one or two ends became broad and straight, some of them irregular with lobed edges, nearly smooth or occasionally with sparse fine warts, measuring 166–419 × 35–181 μm ( Fig. 36B ). Scales in polyp body wall obliquely or transversely arranged, stacked with each other, elongate with an obvious medial contraction, some of them with lobed edges and irregular outline, nearly smooth and rarely with sparse fine warts, measuring 80–502 × 34–230 μm ( Fig. 36D ). Scales in coenenchyme arranged along to the branch, slender, nearly smooth or with one or more large warts, occasionally irregular with lobed edges, measuring 56–516 × 6–84 μm ( Figs. 35G , 36F ). Plates or scales in the mouth area near the tentacles sparse, small and thick with many fine warts, often branched with irregular shape, occasionally rod-like, measuring 45–120 × 7–41 μm ( Fig. 36E ).

Variation of Paratype. For the morphological measurements of paratype, see Table 3 . The specimen of paratype have a longer first internode and more irregular scales in coenenchyme ( Figs. 35G , 37D ).

Type locality. A seamount (tentatively named as M5) on the Caroline Ridge with water depth of 1482 m.

Etymology. The Latin adjective arboriformis (arboriform) refers to the tree-shaped colony of this species.

Distribution and Habitat. Found from the seamounts on the Caroline Ridge in the Western Pacific Ocean with water depths of 1482–1573 m. Colony attached to a rocky substrate ( Fig. 34A, B ). The in-situ water temperature was about 3.08°C and the salinity about 36.45.

Remarks. Chrysogorgia arboriformis sp. nov. has a long unbranched stem with some old scars of the past branches and branches producing on the top forming a tree-shaped colony ( Fig. 34C, D ), which makes it appear to be a member of the chrysogorgiid genus Metallogorgia Versluys, 1902 ( Mosher & Watling 2009). However, the new species matches well with the genus Chrysogorgia with the support of the above morphological features and phylogenetic analyses. It is similar to the species C. abludo Pante & Watling, 2012 , C. dendritica Xu, Zhan & Xu, 2020 , C. fragilis Xu, Zhan & Xu, 2020 and C. gracilis Xu, Zhan & Xu, 2020 by a long unbranched stem, but differs distinctly from them by long toothed rib-like scales in pinnules (vs. absent) ( Pante & Watling 2012, Xu et al. 2020).

Chrysogorgia arboriformis sp. nov. belongs to Versluys’ group C with scales in both tentacle rachis and polyp body wall. Among the species in group C, only six species have long toothed rib-like scales in pinnules, including C. geniculata ( Wright & Studer, 1889) , C. rigida Versluys, 1902 , C. excavata Kükenthal, 1908 , C. cavea Kinoshita, 1913 , C. ramosa Versluys, 1902 and C. arboriformis sp. nov. The new species differs distinctly from the other species by a tree-shaped colony with a long unbranched stem (vs. bottlebrush-shaped colony) ( Wright & Studer 1889, Versluys 1902, Kükenthal 1908, Kinoshita 1913; Table 10 ).

Figures

FIGURE 34. The external morphology and polyps of Chrysogorgia arboriformis sp. nov. A, C. The holotype MBM286465 in situ and after collection. B, D. The paratype MBM286466 in situ and after collection. E, F. A single non-terminal polyp under a light microscope and SEM, respectively. Scale bars: 10 cm (C, D); 1 mm (E, F).

FIGURE 35. The polyps of Chrysogorgia arboriformis sp. nov. A.A part of branch with many polyps under a light microscope. B. Two non-terminal polyps under a light microscope. C–E. Single non-terminal polyps under SEM. F. Tentacular part under SEM. G. A part of branch of the holotype (up) and paratype (down) under SEM, respectively. Scale bars: 5 mm (A); 1 mm (B–E); 500 μm (F, G).

FIGURE 36. Sclerites of the holotype of Chrysogorgia arboriformis sp. nov. A. Sclerites in pinnules. B. Scales at the base of tentacular part. C. Sclerites in tentacle rachis. D. Sclerites in polyp body wall. E. Some small warty sclerites in polyp mouth area near the tentacles. F. Sclerites in coenenchyme. Scale bars: 300 μm (A–F in the same scale); 50 μm (E).

FIGURE 37. Sclerites of the paratype of Chrysogorgia arboriformis sp. nov. A. Sclerites in pinnules. B. Some warty thick sclerites in polyp mouth area near the tentacles. C. Sclerites in tentacle rachis. D. Sclerites in coenenchyme. E. Sclerites at the base of tentacular part. F. Sclerites in polyp body wall. Scale bars: 300 μm (A, C–F in the same scale); 100 μm (B).