Pseudochrysogorgia bellona Pante & France, 2010

Xu, Yu, Zhan, Zifeng & Xu, Kuidong, 2020, Morphology and phylogenetic analysis of five deep-sea golden gorgonians (Cnidaria, Octocorallia, Chrysogorgiidae) in the Western Pacific Ocean, with the description of a new species, ZooKeys 989, pp. 1-37 : 1

Pseudochrysogorgia bellona Pante & France, 2010 Figures 19 , 20 ; Table 3

Pseudochrysogorgia bellona Pante & France, 2010: 595-612.

Type locality.

Bellona Plateau, New Caledonia, 800-923 m depth ( Pante and France 2010).

Voucher specimen.

MBM286490, the Ganquan Plateau in the South China Sea, 586-910 m.

Description.

No whole colony was obtained, thus the description was based on a picture (Figure 19A ) and a few frozen fragments. Colony ca. 50 cm long and 11 cm wide with dendritic holdfast ca. 12 cm long. Main stem more zigzagging. Branching sequences unknown. Branches subdivided dichotomously, up to sixth order with distance between adjacent branches 10-25 mm. Polyps cylindrical, or with an expanded body base and obviously narrow neck, 1.0-2.5 mm long and 0.5-2.5 mm wide at bases, with tentacles up to 1 mm long (Figure 19B-G ).

Rods with many small warts on surface, usually with two round ends and relatively less ornamentation, longitudinally arranged along the back of tentacles, and measuring 142-598 × 11-84 µm (Figures 19H , 20A ). Sclerites in the polyp-body wall including rods, usually with one sharp end, and scales, slightly ornamented, some of them thick and elongated, and measuring 150-620 × 31-127 μm. When the polyp not leaning distad, rods and elongated scales arranged obliquely in the polyp-body wall. While polyps leaning distad, scales mostly arranged longitudinally (parallel to the branch) in upper of body, rods and scales placed obliquely in neck region, and arranged longitudinally on head and the base of tentacles (Figures 19I , 20B ). Scales slightly ornamented, mostly parallel to main branch axis in coenenchyme, and measuring 115-397 × 16-150 μm (Figures 19J , 20C ).

Distribution.

Bellona Plateau, Coral Sea and Otara Seamount, at southern tip of the Kermadec Ridge ( Pante and France 2010, Pante et al. 2012); and South China Sea (present study), 586-1462 m depth.

Remarks.

Pseudochrysogorgia bellona Pante & France, 2010 resembles the species of Chrysogorgia Duchassaing & Michelotti, 1864 by having dichotomously subdivided branches arising from the main stem in a spiraling fashion and forming a bottlebrush-shaped colony. However, it differs in the monopodial or more zigzagging stem (vs. almost sympodial, except Chrysogorgia abludo Pante & Watling, 2012 and C. dendritica Xu, Zhan & Xu, 2020) and obviously different polyps ( Xu et al. 2020). Furthermore, P. bellona is similar to species of Metallogorgia Versluys, 1902 in its monopodial colony and has a close genetic distance as well. However, P. bellona can be separated by its polyps usually with obviously narrow neck (vs. none), dendritic holdfast (vs. discoid) and sclerites including plates, scales and rods with more ornamentation (vs. almost rods and scales with little ornamentation) ( Pante and France 2010). In our specimen, the rods in tentacles are more regular usually with two round ends and less ornamentation. The elongated thick scales are more abundant in coenenchyme, and plates are scarcer than the type colony. We suggest that these differences are population-dependent.

Molecular sequences, genetic distances, and phylogenetic analyses

The conspecific sequences for each newly sampled species were identical, and only the holotype sequence was deposited in GenBank and analysed here. The accession number and the length are as follows: MT269889, 686 bp for Chrysogorgia carolinensis sp. nov., MT269888, 693 bp for C. dendritica , MT050468, 691 bp for M. macrospina ; MT050469, 695 bp for M. melanotrichos , MT050470, 690 bp for P. bellona . The alignment dataset comprised 629 nucleotide positions. Compared to the other Chrysogorgia species, C. carolinensis sp. nov. has six-nucleotide deletion in the mtMust sequence (Figure 21 ). There was no intraspecific variability, while the interspecific distances ranged from zero to 2.42% (Table 4 ). The genetic distances between the new species C. carolinensis sp. nov. and its congeners were in range of 0-2.42%, and those between C. dendritica and its congeners were in the range of 0-1.63%. To date, only three species are available for the genetic distance and phylogenetic analysis for Metallogorgia and Pseudochrysogorgia . The mtMutS genetic distances between M. macrospina and M. melanotrichos was 0.16%, while there was no intraspecific variation within the two species and P. bellona (Table 4 ). The genetic distances between Metallogorgia and Pseudochrysogorgia were 1.94% and 2.10%.

The ML and BI phylogenetic trees are identical in topology, and thus only the former with the both support values is shown (Figure 21 ). In both trees, Metallogorgia , Pseudochrysogorgia , Iridogorgia , Radicipes and Chrysogorgia formed a "monophyletic Chrysogorgiidae clade’’ (MCC) sensu Pante et al. (2012) with moderate to high support (ML 86%; BI 0.95). The Chrysogorgia species were separated into two main clades (Clade I and II) with high support values, which is consistent with Xu et al. (2019, 2020). Clade I includes the sister species C. binata , C. cf. stellata and C. chryseis , and Clade II contains all the rest species. The species C. dendritica and C. abludo formed a sister subclade, followed by C. fragilis . Chrysogorgia carolinensis sp. nov. formed a sister subclade with the cluster C. ramificans + C. monticola , the group C. dendritica + C. abludo + C. fragilis and the rest species within Clade II. Metallogorgia melanotrichos and M. macrospina formed sister clade, followed by P. bellona with full node support (Figure 21 ).

Figures

Figure 19. External morphology and polyps of Pseudochrysogorgia bellona A the colony after collection B-E a single polyp under a light microscope F, G a single polyp under SEM H head of one polyp under SEM I basal polyp body under SEM J coenenchyme under SEM. Scale bars: 10 cm (A), 1 mm (B-G), and 500 μm (H-J).

Figure 20. Sclerites of Pseudochrysogorgia bellona A rods in tentacles B rods and scales in the polyp-body wall C scales in coenenchyme. Scale bar: 300 μm (all images at the same scale).

Figure 21. Maximum likelihood (ML) tree inferred from the mtMutS sequences of Chrysogorgia, Metallogorgia, Pseudochrysogorgia and related species. Numbers at the nodes represent the ML bootstrap values and the posterior probability values of Bayesian analysis (BI). Newly sequenced species are in bold. Support ≤ 50 % / 0.50 is shown as ' -- '. Alignment flatfile showed the mtMutS deletion for Chrysogorgia carolinensis sp. nov. with " - ", using C. averata KC 788265 as a reference.