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

Yu Xu; Zifeng Zhan; Kuidong Xu

doi:10.7717/peerj.8832

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

PeerJ. 2020 Mar 25:8:e8832. doi: 10.7717/peerj.8832. eCollection 2020.

Authors

Yu Xu^{1

2

3

4}, Zifeng Zhan^{1

2

3}, Kuidong Xu^{1

2

3

4}

Affiliations

¹ Laboratory of Marine Organism Taxonomy and Phylogeny, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.
² Laboratory for Marine Biology and Biotechnology, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao, China.
³ Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, China.
⁴ University of Chinese Academy of Sciences, Beijing, China.

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 multi-flabellate 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.

Keywords: Anthozoa; Chrysogorgia dendritica; Chrysogorgia fragilis; Chrysogorgia gracilis; Chrysogorgiidae; Taxonomy.

Grants and funding

This work was supported by the Key Program of National Natural Science Foundation of China (No. 41930533), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA19060401), the Science & Technology Basic Resources Investigation Program of China (2017FY100804) and the Senior User Project of RV KEXUE. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.