Caprella acanthogaster Mayer, 1890 sensu lato (Crustacea: Amphipoda: Caprellidae) has previously been recorded from temperate and cold waters of Far East Asia and Australia. A detailed morphological comparison of specimens collected from Gippsland Lakes (Victoria, Australia) and Otsuchi Bay (Tohoku District, Japan) revealed that C. acanthogaster sensu lato from these regions comprises two separate species. Caprella acanthogaster Mayer, 1890 sensu stricto is confirmed to be distributed in northern Japan. Caprella tamboensis sp. nov. is present in Victoria and Tasmania, Australia, and most noticeably differs from C. acanthogaster sensu stricto in having a relatively short triangular projection on the palm of propodus of gnathopod 2 and a relatively longer peduncle article 2 of antenna 1 (being longer than article 3).