Chrysogorgia ramificans, Xu, Yu, Li, Yang, Zhan, Zifeng & Xu, Kuidong, 2019

Xu, Yu, Li, Yang, Zhan, Zifeng & Xu, Kuidong, 2019, Morphology and phylogenetic analysis of two new deep-sea species of Chrysogorgia (Cnidaria, Octocorallia, Chrysogorgiidae) from Kocebu Guyot (Magellan seamounts) in the Pacific Ocean, ZooKeys 881, pp. 91-107 : 91

Chrysogorgia ramificans sp. nov. Figs 2 , 3

Holotype.

MBM286307, station FX-Dive 174 (17°29.93'N, 153°14.69'E), Kocebu Guyot, depth 1831 m, 8 April 2018. GenBank accession number: MK431863.

Diagnosis.

Chrysogorgia (tertiary "group A, Spiculosae" - rods or spindles in the tentacles and the body wall) with a short basal stem leading to a bottlebrush-shaped main stem, giving of a single major branch also bottlebrush-shaped. Minor branches subdivided dichotomously, up to fourth order, with the first branch internode 20-30 mm long. Branching sequence 1/3R in two large branches and 2/5R in the basal stem. Polyps 2-4 mm tall with a thin neck. Sclerites of polyp body of large and thick rods and spindles with many warts. Small scales and rods in tentacles with many warts. Scales in coenenchyme elongate with irregular edges and a few warts.

Description.

Specimen about 73 cm long with the holdfast not recovered. Main stem forming two large bottlebrush-shaped branches whose axis has a brown metallic luster. The larger branch is 49 cm long and the other 45 cm long. The basal stem about 24 cm long and 4 mm in diameter ( Fig. 2C ). Branching sequences differing from bottom to top, 2/5R in the basal stem and 1/3R in the two large branches. Branches subdivided dichotomously, up to fourth order, the first branch internodes 20-30 mm long, with the terminal branchlets up to 41 mm. Distance between adjacent branches 8-12 mm, and orthostiche intervals about 30 mm in the two large branches and 50 mm at the bottom. Polyps thin, about 2-4 mm long and 1.0-1.5 mm wide at bases, with a long neck less than 1 mm wide. Two to four polyps on the first internodes, up to eight on terminal branchlets ( Fig. 2D ). No polyps on main axis internodes.

Rods and spindles of base of polyp body wall large and thick, rarely branched, with many warts on surface, and measuring 247-628 × 109-180 μm, with an average of 430 × 136 μm ( Figs 2D , 3C ). Rods and spindles longitudinally arranged in the polyp neck extending to the rachis of tentacles, all covered with many warts, and measuring 95-520 × 25-96 μm, with an average of 304 × 54 μm ( Fig. 3A ). Scales of pinnules small with coarse edges and many warts on surface, and measuring 114-214 × 29-49 μm, with an average of 146 × 36 μm ( Fig. 3B ). Scales elongated and flat in coenenchyme with dentate edges and a few warts, and measuring 139-553 × 35-87 μm, with an average of 267 × 61 μm ( Fig. 3D ).

Etymology.

The Latin adjective ramificans (branching) refers to the ramous structure of the stem.

Distribution.

Found only from the Kocebu Guyot with water depth of 1831 m.

Habitat.

Colony attached to a rocky substrate with a small, oval-shaped holdfast ( Fig. 2A ).

Remarks.

Chrysogorgia ramificans sp. nov. differs from all known congeners by its main stem, with 2/5R branching sequence, forming two large bottlebrush-shaped branches with 1/3R branching sequence ( Cairns 2001, 2018; Pante and Watling 2011). The new species belongs to the Chrysogorgia "group A, Spiculosae", in which it mostly resembles C. monticola Cairns, 2007. However, C. ramificans sp. nov. differs from C. monticola by the much longer interval of adjacent branches (8-12 mm vs. 4-5 mm), longer first internode of branch (20-30 mm vs. 12 mm), larger polyps (2-4 mm vs. 1.1 mm in height), much wider rods (109-180 μm vs. 50-80 μm) with thick ends and warty surface in the body walls (vs. with thin ends and usually smooth surface), and small and unbranched rods at the tentacle base (vs. large and lobed) ( Cairns 2007).

Within the group A, Chrysogorgia ramificans sp. nov. is also similar to C. arborescens Nutting, 1908, C. tuberculata Cordeiro et al., 2015 and C. terasticha Versluys, 1902. However, the new species differs from C. arborescens by its much longer interval of adjacent branches (8-12 mm vs. 3 mm), the higher number of polyps in the distal branchlets (up to 8 vs. 2), and usually regular sclerites (vs. irregular) ( Nutting 1908). It differs from C. tuberculata by the larger orthostiche intervals (30-50 mm vs. 8-23 mm), rods with numerous coarse warts (vs. spindles with acute and sparse warts), rods present in tentacles (vs. only scales), and scales in coenenchyme with inconspicuous warts (vs. prominent) ( Cordeiro et al. 2015). The new species can be easily distinguished from C. terasticha by its branching sequence (1/3R at top and 2/5R at bottom vs. 1/4L), larger orthostiche intervals (30-50 mm vs. no more than 8 mm), no nematozooids in coenenchyme (vs. many), larger polyps (2-4 mm vs. no more than 1.6 mm), larger rods with various ends (vs. smaller with rounded ends), and the absence of scales at the polyp base (vs. presence) ( Versluys 1902).

Figures

Figure 2. External morphology and polyps of Chrysogorgia ramificans sp. nov.: A The holotype in situ B Close-up of branches and polyps in situ C The colony after collection D A single polyp under light microscope E Single polyp under SEM. Scale bars: 20 cm (C); 1 mm (D, E).

Figure 3. Sclerites of Chrysogorgia ramificans sp. nov. A Sclerites of polyp neck extending to the rachis of tentacles B Sclerites in the pinnules C Sclerites at the body base D Sclerites of coenenchyme. Scale bars: 200 μm (A, C, D); 50 μm (B).