A new eyeless species of Nereis (Annelida, Nereididae) from deep-sea sediments of the northern South China Sea

A variety of nereidid species have been reported from the South China Sea, although little is known about the deep-sea species in this area. Recently, two specimens belonging to a novel nereidid polychaete were collected from a sedimentary habitat during an environmental survey to a deep-sea basin where cold seeps occur. This new species, Nereis tricirrata sp. nov., is described herein, based on morphologi-cal and molecular analyses. The most noteworthy feature is the absence of eyes on the prostomium; it can be distinguished from other eyeless Nereis species by the arrangement of conical paragnaths on the pharynx, the nature of homogomph falcigers and the shape of notopodial lobes in posterior chaetigers. The reconstructed phylogenetic tree, using concatenated sequences of mtCOI, 16S, and 18S rRNA, showed that all Nereis species included in this study form a monophyletic clade with full support. The mtCOI-based interspecific comparisons revealed a high genetic divergence (23.1%-37.3% K2P) from four-eyed Nereis species with the available sequences. This is the first record of an eyeless Nereis species in the South China Sea.

Automated summary

This study reports the discovery of a new eyeless polychaete species, Nereis tricirrata, in the South China Sea. The species is described based on morphological and molecular analyses, and is distinguished from other eyeless Nereis species by several unique features. The phylogenetic analysis shows that all Nereis species form a monophyletic clade, and the interspecific comparisons reveal high genetic divergence.