Three synonyms of the coastal Phucobius sharp species (Coleoptera: Staphylinidae) are proposed based on morphological and molecular characters

A taxonomic reappraisal of four marine littoral Phucobius Sharp species along the western Pacific Ocean including the South China Sea is presented based on morphological and molecular characters (COI and 28S). Specimens of the four species, each having its own distinct geographic distribution, are extremely similar to each other including the structures of the median lobe of the aedeagus, and may be regarded as conspecific. Also, the molecular analyses support the validity of P. pectoralis with three synonymies based on morphological characters. Genetic divergence of COI using uncorrected p-distance among all individuals of Phucobius species ranged from 0.11% to 3.21%. Three distinct geographical clusters (Russia, Korea and Japan, and Vietnam) are found in the NJ and PA trees and we treat all of them as a single species. Three new synonyms are proposed for Phucobius pectoralis (Boheman): P. simulator Sharp syn. nov., P. tricolor Bernhauer syn. nov., and P. densipennis Bernhauer syn. nov. Phucobius pectoralis is redescribed with illustrations of diagnostic characters. Also, the intraspecific variation among the populations of P. pectoralis is briefly discussed.