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.
Highlights
The genus Chrysogorgia Duchassaing & Michelotti, 1864 contains 72 species distributed in the world oceans, with water depths ranging from 10 m to 4,492 m (Watling et al, 2011; Pante et al, 2012; Cairns, 2018; Xu et al, 2019)
Three branching forms have been recognized in the colonies of the genus: a single ascending spiral producing a bottlebrush shape, a single fan and two fans emerging from a short main stem (Pante & Watling, 2012; Cordeiro, Castro & Pérez, 2015)
Based on morphological and phylogenetic analyses, we describe these specimens as three new species: C. dendritica sp. nov., C. fragilis sp. nov. and C. gracilis sp. nov
Summary
The genus Chrysogorgia Duchassaing & Michelotti, 1864 contains 72 species distributed in the world oceans, with water depths ranging from 10 m to 4,492 m (Watling et al, 2011; Pante et al, 2012; Cairns, 2018; Xu et al, 2019). Based on the shapes of rods or scales in the body wall and tentacles, a rough grouping has been built for the separation of Chrysogorgia species. Versluys (1902) divided the genus Chrysogorgia into three groups, which were summarized by Cairns (2001) as ‘‘group A, Spiculosae’’, ‘‘group B, Squamosae aberrantes’’, and ‘‘group C, Squamosae typicae’’. Based on morphological and phylogenetic analyses, we describe these specimens as three new species: C. dendritica sp. Their genetic distances and single mutations on mtMutS as well as phylogenetic relationships within Chrysogorgia species are discussed
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