Review of the Gnathiidae (Crustacea: Isopoda) of western Japan with a description of five new species, one redescription, and one new Japanese record

The gnathiid fauna around the world, including Japan, remains poorly detailed in the literature. In this study, we examine gnathiid specimens obtained from the continental shelf area of western Japan from 1995 to 2023. As a result, we report the following findings: (1) two new species of Caecognathia : Caecognathia tida sp. nov. and Caecognathia inferoculus sp. nov.; (2) three new species of Gnathia : Gnathia hayashiae sp. nov., Gnathia toyoshiomaruae sp. nov., and Gnathia tajirana sp. nov.; (3) redescription of Gnathia consobrina (Monod, 1926) comb. nov. since the original description; and (4) first record of Gnathia koreana Song and Ming, 2018 from Japan. Most descriptions are based on male specimens but female and third stage praniza larva are described in G . hayashiae sp. nov. New distributional records are given for Gnathia camuripenis Tanaka, 2004, Gnathia kumejimensis Ota, 2012, and Thaumastognathia tanseimaruae Shimomura and Tanaka, 2008. Keys to genera of Gnathiidae and the Japanese species of Caecognathia and Gnathia are provided.