Mediomastus chinensis sp nov., a new species of Capitellidae (Annelida: Polychaeta) from the southeast coast of China

Mediomastus is a common genus around the world, and Chinese specimens used to be identified as M. californiensis Hartman. In this study, 118 Mediomastus specimens collected from four localities along the southeast coast of China were examined. They belonged to an unknown species. We treat them as a new species, described herein. The new species is characterized as follows: (1) chaetigers 1-9 biannulate with chaetal fascicles at midsegment, thereafter multiannulate with chaetal fascicles posterior to midsegment; (2) parapodial ridges on posterior abdomen; (3) possession of bilimbate capillary chaetae on chaetigers 1-4; (4) thoracic hooks with long, straight shaft, hood length about 3-5 times width; (5) abdominal hooks shorter, with developed shoulder and distinct constriction, markedly different from those in thorax; (6) unique staining pattern with methyl green. The present study indicated that Mediomastus species inhabiting Chinese waters might be misidentified as M. californiensis, and that Mediomastus chinensis sp. nov. is widely distributed along the southeast coast of China.