Abstract:Six naupliar stages of Tigriopus japonicus Mori, 1932 are described from the rocky coast off Keelung, northeastern Taiwan. A key for the identification of stages is provided. Naupliar morphology within the Harpacticidae differs among species and even more at the supraspecific level. The present study on nauplii of Tigriopus japonicus confirms the observation that representatives of the Tachidiidae and Harpacticidae (Copepoda-Harpacticoida) show a peculiar reduction of the oral structures from N V to N VI. The nauplii of the Harpacticidae are creeping larvae, and many are not able to swim; however, nauplii of T. japonicus are an exception to this rule.