熱帯西太平洋の海山から発見された深海新種(Cnidaria, Octocorallia)3種の形態と分子系統

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

• Yu Xu
• Zifeng Zhan
• Kuidong Xu

抄録

本研究では，西太平洋熱帯海域の海山から3種の新種を発見した．はマリアナ海溝に隣接する水深 298 m の海山から採集された。これらはいずれも体壁と触手に棒が分布する「A 群, Spiculosae」に属し，樹形のコロニーを持つ点で Pante & Watling, 2012 を除くすべての近縁種とは異なる。sp. nov.は一脚性の茎を持つこと，1/3L分岐列を持つこと，ポリプの体基部にアメーバ状の強膜（強膜は多方向に向かって分岐する）を持つことに特徴がある。に最もよく似ているが，1/3L分岐配列が規則的であることと，副生体の鱗片が細長いことで異なる。mtMutS遺伝子の系統解析と遺伝的距離解析に基づいて、利用可能な全種を2つのグループに分けた。1つは、短い主幹から2本以上の扇形が出ているもの（2本または多本の扇形コロニー）、もう1つは、単一の上昇螺旋状（時計回りまたは反時計回り、ボトルブラシ型コロニー）、扇形（平面コロニー）、および長い直線の幹の上に枝の茂みがあるもの（樹木型コロニー）である。さらに、木型コロニーは、次のような新しい分岐パターンを示すことから、一般的な診断を拡張している。

Three new species of were discovered from seamounts in the tropical Western Pacific Ocean. sp. nov. and 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 sp. nov. was collected from a seamount adjacent to the Mariana Trench with the water depth of 298 m. They all belong to the "group A, Spiculosae" with rods distributed in body wall and tentacles, and differ from all congeners except Pante & Watling, 2012 by having a tree-shaped colony (vs. bottlebrush-shaped, planar or biflabellate). 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. sp. nov. is most similar to , but differs by the regular 1/3L branching sequence and elongate flat scales in coenenchyme. 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 species were separated into two main groups: one includes , cf. and , 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 , and therefore we extend the generic diagnosis.

©2020 Xu et al.