A New Species of <i>Caprella</i> (Crustacea: Amphipoda: Caprellidae) Collected from Ehime Prefecture, Western Japan

A new species of Caprella Lamarck, 1801 (Crustacea: Amphipoda: Caprellidae) collected from the rocky coasts of Ehime Prefecture, western Japan, is described. The sampling site of the present new species is adjacent to the district where organic citrus cultivation is predominant. Of the approximately 200 species of Caprella, the present species, C. gracilenta sp. nov., is most closely related to C. rhopalochir Mayer, 1890. The type locality of C. rhopalochir is the mouth of the Amur River, located at the northern end of the Sea of Japan. In addition, C. rhopalochir was recorded until the 1970s from northern Kyushu and adjacent areas near the southwestern end of the Sea of Japan, where oceanographic conditions are largely different from the type locality of C. rhopalochir. Caprella gracilenta sp. nov. is distinguished from C. rhopalochir by the absence of forwardly curved triangular projection near the posterior end of pereonite 1, triangular projection on the dorsal face of the propodus of gnathopod 2, paired dorsal projections on pereonites 3–4, and triangular projection near the posterior end of pereonites 3–4. Of the two descriptions of C. rhopalochir from near the southwestern end of the Sea of Japan, a description from Saga Prefecture was identified as C. gracilenta sp. nov. This re-identification indicates that C. gracilenta sp. nov. is a rare species widely distributed along the western coast of Japan.