Chaetarthria saundersi d'Orchymont, 1923 is recorded from Iriomote-jima Island, Okinawa Prefecture, Japan. This represents the first record of the genus Chaetarthria from Japan as well as the tribe Chaetarthriini sensu Short and Fikáček (2013). This genus is very easily distinguished from other Japanese hydrophilids by strongly convex body and the presence of a fringe of setae on the first abdominal ventrite.