A new species of the genus Hydrovatus Motschulsky (Coleoptera: Dytiscidae) from Japan

Hydrovatus onigiri Watanabe and Bistrom, new species is described from Japan. The new species is similar to Hydrovatus subtilis Sharp. 1882, but it is distinguishable from the latter by male antennomeres 4-6 being the broadest (rather than anten-nomeres 6-8), poorly developed male stridulatory apparatus, and an almost evenly curved penis apex. Hydrovatus onigiri, new species is the 20th species of the H. confertus species group, and 10th Hydrovatus Motschulsky species known from Japan.