A new species of Arabella (Annelida, Polychaeta, Oenonidae) from the sea off Gouqi Island, Zhejiang, China

Arabella is the second-most diverse genus in the family Oenonidae, with about 50 species known so far. However, until now, there has been no detailed taxonomic information on Arabella species in the East China Sea. In this study, we describe a new species, Arabella gouqi sp. nov., discovered in the sea off Gouqi Island, Zhejiang, China, using integrated morphological and molecular evidence.

This species is characterized by the following features: a pygidium with two swollen pads, short notopodial cirri, a bifid robust left and a gracile falcate right maxilla I (MxI), short left and long right maxilla II (MxII), a posterior postchaetal lobe shorter than the chaetae, and gradually tapering of the ventralmost chaetae. Phylogenetic analysis based on both COI and 16 S rDNA gene sequences showed that A. gouqi sp. nov. forms a distinct, fully supported monophyletic clade.

These findings were further supported by substantial Kimura 2 - parameter (K 2 P) genetic distances between the new species and other reported Arabella species, which ranged from 9.9 % to 24.2 % for COI and from 5.5 % to 25.2 % for 16 S rDNA. This study provides essential data for understanding the taxonomy of Arabella in the East China Sea and emphasizes the need for further research on this group in the region.