Parachrysogorgia, 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 : 20

Genus Parachrysogorgia gen. nov.

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Diagnosis. Colony branching sympodial, arising from a single ascending spiral (counterclockwise, bottlebrush-shaped colony), two or more fans emerging from a short main stem (bi- or multi-flabellate colony). Axis with a metallic shine. Branch subdivided dichotomously or with branchlets forming a sympodium. Polyps relatively large and stout, with a bare, sclerite-free area at the base of each tentacle and eight distinct projections (acuminate or warty) beneath tentacles. Sclerites in the form of scales in polyp body wall, spindles/rods, and/or scales in tentacles.

Type species. Parachrysogorgia chryseis ( Bayer & Stefani, 1988) comb. nov. (basionym: Chrysogorgia chryseis Bayer & Stefani, 1988 ).

Distribution. Currently known only from the Pacific and North Atlantic Oceans, 329–1937 m.

Species assigned. Thirteen species of Chrysogorgia are transferred to Parachrysogorgia . These are P. admete ( Bayer & Stefani, 1988) comb. nov., P. antarctica ( Cairns, 2002) comb. nov., P. binata ( Xu, Li, Zhan & Xu, 2019) comb. nov., P. bracteata ( Bayer & Stefani, 1988) comb. nov., P. calypso ( Bayer & Stefani, 1988) comb. nov., P. chryseis ( Bayer & Stefani, 1988) comb. nov., P. electra ( Bayer & Stefani, 1988) comb. nov., P. expansa ( Wright & Studer, 1889) comb. nov., P. octagonos ( Versluys, 1902) comb. nov., P. scintillans ( Bayer & Stefani, 1988) comb. nov., P. squamata ( Verrill, 1883) comb. nov., P. stellata ( Nutting, 1908) comb. nov., and P. versluysi ( Kinoshita, 1913) comb. nov. Other species (e.g., C. intermedia Versluys, 1902 , C. curvata Versluys, 1902 ) with incomplete descriptions need to be confirmed based on detail morphological examination as well as phylogenetic analyses.

Remarks. Untiedt et al. (2021) recognized nine distinct morphological groups of Chrysogorgia s.l. and hypothesized that each likely represents a distinct genus by using a concatenated UCE and exon loci dataset ( Table 4 ). Our previous phylogenetic analysis based on mtMutS gene data showed that all the available species of Chrysogorgia were clustered into two Clades (I and II), and the genetic distances between Clades I and II (the main Chrysogorgia clade) were much higher than the intra-clade ones of Clade II ( Xu et al. 2020a). The newly constructed mtMutS - COI gene and 28S rDNA trees further support the separation of the usual Chrysogorgia species from the new genus Parachrysogorgia ( Figs. 1 , 2 ). Parachrysogorgia is morphologically separated from Chrysogorgia by possessing a bare, sclerite-free area present at the base of each tentacle and eight distinct acuminate or warty projections beneath the tentacles. The two features can be easily observed under a bright microscope and are distinct under a scanning electronic microscope (SEM). Both the morphological and molecular data justify the establishment of the new genus.

Parachrysogorgia shares similar external morphology with certain species of Chrysogorgia in having a bottlebrush-shaped colony with a counterclockwise spiral, or bi- or multi-flabellate colony, while Chrysogorgia also contains species with a clockwise spiral, or a planar or tree-shaped colony.

Etymology. Composition of the Greek prefix para (similar to) and the generic name Chrysogorgia , referring to the similarity of the new genus with Chrysogorgia . Feminine gender.

Figures

FIGURE 1.Maximum likelihood(ML) tree constructed by the concatenated sequencesof mtMutS andCOI showingphylogenetic relationships among Parachrysogorgia and Chrysogorgia species. The Bayesian inference (BI) tree is identical to the ML tree in topology. Node support is as follows: ML bootstrap / BI posterior probability. The ML bootstrap <70 or BI posterior probability <0.90 is not shown. New sequences are in bold. The GenBank accession numbers of the mtMutS sequences were listed next to the species names.

FIGURE 2. Maximum likelihood (ML) tree constructed by 28S rDNA showing phylogenetic relationships among Parachrysogorgia and Chrysogorgia species. The Bayesian inference (BI) tree is identical with the ML tree in topology. Node support is as follows: ML bootstrap / BI posterior probability. The ML bootstrap <70% or BI posterior probability <0.90 is not shown. New sequences are in bold. The GenBank accession numbers of the 28S rDNA sequences were listed next to the species names.