Ophelia yangi sp. nov. (Annelida, Opheliidae), a new species from Chinese waters, with comments on the taxonomic characters of the genus

Ophelia limacina (Rathke, 1843), originally described from Norway, is the only species of Ophelia Savigny, 1822 recorded from Chinese waters, but these records have never been verified. To clarify the identity of the Chinese Ophelia , specimens from the Chinese coast, from Shandong to Fujian, were examined. They differ from O. limacina and from all other congeners and are described here as Ophelia yangi sp. nov .; the earlier Yellow Sea record of O. cf. limacina is also tentatively referred to the new species. The new species has 32 chaetigers with the body formula 10a + 16b + 6a, i.e., ten anterior abranchiate, 16 branchiate, and six posterior abranchiate chaetigers, and simple cirriform branchiae; branchial fenestrations are present. The body formula was constant in all specimens examined, except on one side of one of 20 specimens. In the mitochondrial cytochrome c oxidase subunit I (COI) and 16S rRNA genes, the new species differs from all other sequenced taxa of Ophelia by uncorrected p-distances of 15.6–16.5% (COI) and 6.4–7.8% (16S), whereas the maximum intraspecific COI distance is 0.5%. The variation observed in the examined specimens was used to evaluate the characters that have been used to distinguish species of Ophelia . The body formula was stable in these specimens, whereas the length of the branchiae, the posterior dorsal longitudinal ridges, the origin of the ventral groove, and the nephridiopores varied among specimens or were difficult to observe in preserved material; these characters should therefore be used with caution.