The genus Rhynchospio has fronto-lateral horns on prostomium, paired branchiae from chaetiger 2 to near the posterior end, capillary notochaetae only, and more than two pairs of pygidial cirri. Rhynchospio species are common in coastal soft bottom communities; nevertheless, many recorded Rhynchospio specimens around the world are currently undescribed. Here we described a Rhynchospio species based on specimens collected from Qingdao, China. Comparison with the reported DNA sequences of four gene markers (16S rRNA, 18S rRNA, 28S rRNA, and Histone H3) and brief morphological description of specimens collected from Jinhae Bay, South Korea, previously reported as Rhynchospio aff. asiatica , indicated that they are conspecific. Morphologically, specimens of R . aff. asiatica from Qingdao are characterized by having neuropodial hooded hooks from chaetigers 14–17 (vs. 10–23 in R . asiatica ) to near pygidial chaetigers, sperm from chaetiger 11 to 14 (vs. from chaetiger 11 to 21–22 in R . asiatica ), oocytes from chaetigers 16–17 to 26–39 (vs. from 22–24 in R . asiatica ), and 4–6 (vs. up to 6 in R . asiatica ) pygidial cirri. Genetically, Rhynchospio aff. asiatica is most closely related to R . arenincola Hartman, 1936 from California, USA with the interspecific distances of 20.02％ (16S rRNA), 4.50％ (18S rRNA), 8.44％ (28S rRNA), 2.74％ (Histone H3), and 6.10％ (concatenated sequences). Water flow across the dorsum created by ciliary beating of the branchiae and nototrochs, observed on live specimens, may help transport gametes from reproductive segments in anterior and middle parts to the posterior brooding segments. Phylogenetic trees based on concatenated sequences of four gene markers of 54 spioniform species in 25 genera revealed two clades, covering the two subfamilies Spioninae and Nerininae respectively. Two families (i.e., Poecilochaetidae and Trochochaetidae) in the order Spionida were clustered within Spionidae, supporting a morphology-based proposal that these families bearing a pair of prehensile, grooved palps should be grouped within a more broadly defined family Spionidae. Mapping morphological and reproductive characteristics to the phylogenetic trees indicated that the ancestor of spionids might lack branchiae, broadcast spawn thick-envelop oocytes and ect-aquasperm, and produce planktotrophic larvae.

Zhi WANG;Ting XU;Jian-Wen QIU;Yinglu JI;Zishan YU;Caihuan KE

State Key Laboratory of Marine Environmental Science,College of Ocean and Earth Sciences,Xiamen University,Xiamen 361102,China;Department of Ocean Science and Hong Kong Branch of the Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou),Hong Kong University of Science and Technology,Hong Kong 999077,China;Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou),Guangzhou 511458,China;Department of Biology and Hong Kong Branch of the Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou),Hong Kong Baptist University,Hong Kong 999077,China;North China Sea Marine Forecasting Center of State Oceanic Administration,Qingdao 266061,China;College of Marine Life Sciences,Ocean University of China,Qingdao 266003,China

海洋湖沼学报（英文版）

[1]Zhi WANG;Ting XU;Jian-Wen QIU;Yinglu JI;Zishan YU;Caihuan KE-.Morphological analysis of Rhynchospio aff. asiatica (Annelida: Spionidae) and comments on the phylogeny and reproduction of the family Spionidae)[J].海洋湖沼学报（英文版）,2022(03):1257-1276

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