Three species of marine hatchetfishes, Sternoptyx diaphana Hermann, S.obscura Garman, and S.pseudobscura Baird, were reported from the western North Pacific Ocean, based upon the materials collected by the R/V Tansei-Maru and Hakuho-Maru, Ocean Research.Institute, University of Tokyo.
The morphological differences among the three species were tested by the statistical method proposed by Ito (1953) to test slope and positional differences of allometry line and proved to be significant at risk of 1 % level in many characters as presented in Table 3.These support the results of Baird (1971) who recognized three species in the genus Sternoptyx which had been usually treated monotypic.The key to the species in the western North Pacific Ocean are as follows.