Description of a new Promastobranchus species (Annelida, Capitellidae) from Chinese coasts, with molecular evidence for intraspecific variation in the number of thoracic chaetigers.

Promastobranchus Gallardo, 1968 is a small genus in the polychaete family Capitellidae, and the available records are largely reported from the Indo-West Pacific region. Although Gallardo (1968) and Green (2002) noted that Promastobranchus species had intraspecific variation in the number of thoracic chaetigers when they described the two previously known species, this variation has not been corroborated using molecular evidence. In this study, a new Promastobranchus species, Promastobranchusvariabilissp. nov., is described based on 29 specimens collected from the Beibu Gulf, South China Sea. The new species is mainly characterized by having a tessellated epithelium in the anterior thorax, nine teeth in three rows above the main fang in the abdominal hooks, four pairs of genital pores located on the intersegmental grooves between chaetigers 9 and 13, and its unique methyl green staining pattern. Comparisons of multiple gene markers (16S, 18S, 28S, and H3) revealed no genetic divergence (K2P < 0.003) among these type specimens with 9-13 thoracic chaetigers. In other words, the new species exhibited morphological variability in the number of thoracic chaetigers during ontogeny, and this character was unsuitable to differentiate Promastobranchus species as the ranges overlap among Promastobranchus species. This is the third Promastobranchus species known in the world, and it is now recorded along the Fujian coast.

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, Nereistricirrata sp. nov., is described herein, based on morphological 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.

A new species of Leiochrides Augener, 1914 (Annelida: Capitellidae) from the Beibu Gulf, South China Sea.

BACKGROUND: Polychaetes of the family Capitellidae are poorly studied in Chinese waters. Amongst the known capitellid genera in China, Leiochrides Augener, 1914 is an unusual genus encountered in marine surveys. NEW INFORMATION: In this study, a Leiochrides specimen was obtained during a survey conducted in the Beibu Gulf, northern South China Sea and described herein as a new species Leiochrides guangxiensis sp. nov. The new species differs from its congeners by having uniramous chaetiger 1, chaetigers 11-12 with notopodial capillaries and neuropodial hooks, abdominal hooks with seven teeth above the main fang in three rows, pygidium with four anal cirri, and branchial fascicles with up to 17 filaments. The taxonomic status of the monospecific genus Pseudoleiocapitella Harmelin, 1964 and Leiochrides norvegicus Fauchald, 1972 are discussed.

A new species of Notomastus (Annelida, Capitellidae) from southern China, with remarks on its morphology and distribution.

The genus Notomastus is frequently encountered in Chinese waters. However, its species richness is poorly understood. In this study, a Notomastus species obtained from Xiamen Bay, southern China, was described and illustrated as a new species (N. sunae sp. nov.), based on morphological and molecular analyses. The new species is characterized by having uniramous chaetiger 1, the presence of palpode and eyespots on prostomium, chaetiger 11 with notopodial capillaries and neuropodial hooded hooks, and notopodial lobes with simple epithelial extensions on far posterior abdomen. With additional specimens collected from several localities along the southern coasts of China, the morphology and geographical distribution of the new species are discussed. A key is also provided for Notomastus species with neuropodial hooks in thoracic chaetiger 11.