Taxonomy And Phylogeny Of The Golden Coral Family Chrysogorgiidae(Anthozoa:Alcyonacea) From Seamounts In The Western Pacific

The family Chrysogorgiidae(Cnidaria,Anthozoa,Octocorallia,Alcyonacea,Calcaxonia)is distributed in the global ocean,including 14 genera and 112 recorded species at present.Except a few species growing in the coastal waters,most chrysogorgiids are living in the deep water and hard bottom of the seamounts or continental slopes.At present,there are only six genera including Pleurogorgia,Radicipes,Metallogorgia,Stephanogorgia,Chrysogorgia and Pseudochrysogorgia found in the Western Pacific.In China,systematic classification of chrysogorgiids have not yet been carried out,and only two unidefined species were recorded in the East China Sea.Seamounts with their unique habitat have been the hotspot of deep-sea biodiversity research and protection.There are numerous seamounts in the tropical Western Pacific,where only a few have been explored.Since 2016,we have collected 23 chrysogorgiid specimens from three seamounts by ROV Faxian(Discovery)during the cruises of the R/V Kexue(Science)in the tropical Western Pacific.Based on these specimens,we carried out a systematic study about taxonomy and phylogeny.Based on the summaries about the research backgrounds for each taxon and a large number of literatures,this study made detailed morphological descriptions for all species,including the external morphology,branches,polyps and sclerites in different parts.And it also provided identification keys to each genus and species,and the information on their geographical distribution.A total of 24 specimens of chrysogorgiids were identified as 4 genera(Chrysogorgia,Metallogorgia,Iridogorgia and Rhodaniridogorgia)and 16 species,including 9 new species(Chrysogorgia fascicularis n.sp.,Chrysogorgia binata n.sp.,Chrysogorgia ramificans n.sp.,Chrysogorgia stipitiformis n.sp.,Chrysogorgia fragilis n.sp.,Chrysogorgia gracilis n.sp.,Iridogorgia densispicula n.sp.,Iridogorgia squarrosa n.sp.and Rhodaniridogorgia macroclada n.sp.)The octocoral mtMutS gene codes for a protein with all the necessary components for DNA mismatch repair.The phylogenetic trees of four species were constructed in this study by using mtMutS gene sequencing.Based on the phylogenetic analysis,the genetic distances of mtMutS between I.densispicula n.sp.and congeners are much higher than those among the rest congeners.And I.densispicula n.sp.branched early with a single basal clade within Iridogorgia with full node support in the phylogenetic trees,supporting the effectiveness of the new species.Molecular phylogenetic analysis indicates that I.squarrosa n.sp.,C.ramificans n.sp.and C.binata n.sp.are clustered with some species with high support,and difficult to separate with them by genetic distances and phylogenetic tree,indicating their close relationships.In this study,the diversities of chrysogorgiids in seamounts of the tropical Western Pacific and a few unknown deep-sea new species are revealed and described,which provides a reference for the hypothesis about seamount biodiversity distribution pattern.It is of great significance to explore and ultilize the deep-sea biological resources by exploring the evolutionary relationship of chrysogorgiids,enriching the sequences of the GenBank and the species information.