All Japanese species attributed to the genera Eunice and Euniphysa are studied taxonomically with or without new records. The species erected by Moore (1903) are redescribed to correct his confusing descriptions caused by his unique counting method of body segments. Using the specimens collected chiefly by the cruise of R/V "Tansei-Maru" of the Ocean Research Institute, fhe new species and one new subspecies are described. For several species with enough number of specimens, the variability of morphological characters such as the occurrence of branchiae and subacicular hooks, is examined statistically and the ontogenetic change of the branchial distribution is mentioned. For twenty species, their precise distribution of branchiae is shown. Possible pathways of modifications occurring in the branchial distribution patterns are discussed.