Morphology and molecular phylogeny of three new deep-sea species ofChrysogorgia(Cnidaria, Octocorallia) from seamounts in the tropical Western Pacific Ocean

Abstract

Three new species of Chrysogorgia were discovered from seamounts in the tropical Western Pacific Ocean. Chrysogorgia dendritica sp. nov. and Chrysogorgia fragilis sp. nov. were collected from the Kocebu Guyot of the Magellan Seamount chain with the water depth of 1,821 m and 1,279-1,321 m, respectively, and Chrysogorgia gracilis sp. nov. was collected from a seamount adjacent to the Mariana Trench with the water depth of 298 m. They all belong to the Chrysogorgia ''group A, Spiculosae'' with rods distributed in body wall and tentacles, and differ from all congeners except C. abludo Pante & Watling, 2012 by having a tree-shaped colony (vs. bottlebrush-shaped, planar or biflabellate). Chrysogorgia dendritica sp. nov. is unique in having a monopodial stem, the 1/3L branching sequence and the amoeba-shaped sclerites (sclerites branched toward to many directions) at the body bases of polyps. Chrysogorgia fragilis sp. nov. is most similar to C. abludo, but differs by the regular 1/3L branching sequence and elongate flat scales in coenenchyme. Chrysogorgia gracilis sp. nov. is easily separated from congeners by the 1/4L branching sequence, the absence of sclerites in the basal body wall, and the very sparse scales in coenenchyme. Based on the phylogenetic and genetic distance analyses of mtMutS gene, all the available Chrysogorgia species were separated into two main groups: one includes C. binata, C. cf. stellata and C. chryseis, which have two or more fans emerging from a short main stem (bi-or multiflabellate colony); the other one includes all the species with the branching patterns as a single ascending spiral (clockwise or counterclockwise, bottlebrush-shaped colony), a fan (planar colony) and a bush of branches perched on top of a long straight stem (tree-shaped colony). Additionally, the tree-shaped colony represents a new branching pattern in Chrysogorgia, and therefore we extend the generic diagnosis.How to cite this article Xu Y, Zhan Z, Xu K. 2020. Morphology and molecular phylogeny of three new deep-sea species of Chrysogorgia (Cnidaria, Octocorallia) from seamounts in the tropical Western Pacific Ocean. PeerJ 8:e8832 http://doi.

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

“…In both trees, Metallogorgia, Pseudochrysogorgia, Iridogorgia, Radicipes and Chrysogorgia formed a "monophyletic Chrysogorgiidae clade'' (MCC) sensu 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 (2019Xu et al ( , 2020. Clade I includes the sister species C. binata, C. cf.…”

“…The barcoding analysis of mtMutS is considered as the first step in molecular identification of octocorals (McFadden et al 2011;. However, the mtMutS genetic distances within Chrysogorgia are relatively low, and there is no barcoding gap (intraspecific zero vs. interspecific 0-2.42%) for species identification, as shown by Xu et al (2020). Thus, the discrimination of the closely related species was mainly relied on other molecular evidence and morphological characters.…”

“…However, it differs in the monopodial or more zigzagging stem (vs. almost sympodial, except Chrysogorgia abludo 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.…”

“…The genus Chrysogorgia Duchassaing & Michelotti, 1864 contains 75 species and is distributed worldwide (Watling et al 2011;Cairns 2018;Xu et al 2020). It is characterized by four branching forms of the colony, including a single ascending spiral (clockwise or counterclockwise, bottlebrush-shaped colony), a single fan (planar colony), two or more fans emerging from a short main stem (bi-or multi-flabellate colony) and a bush of branches perched on top of a long straight stem (tree-shaped colony) Cordeiro et al 2015;Xu et al 2020).…”

“…The genus Chrysogorgia Duchassaing & Michelotti, 1864 contains 75 species and is distributed worldwide (Watling et al 2011;Cairns 2018;Xu et al 2020). It is characterized by four branching forms of the colony, including a single ascending spiral (clockwise or counterclockwise, bottlebrush-shaped colony), a single fan (planar colony), two or more fans emerging from a short main stem (bi-or multi-flabellate colony) and a bush of branches perched on top of a long straight stem (tree-shaped colony) Cordeiro et al 2015;Xu et al 2020). Based on the shapes of rods or scales in the polyp-body wall and tentacles, four groups have been recognized for the separation of Chrysogorgia species, including "group A, Spiculosae" with 42 species, "group B, Squamosae aberrantes" with 13 species, "group C, Squamosae typicae" with 19 species and "group D, Spiculosae aberrantes" with only one species (Versluys 1902;Cairns 2001;Cordeiro, Castro and Pérez 2015;Xu et al 2019).…”