japonicum, Sicydium Tanaka [S.] 1909:22 [Journal of the College of Science. Imperial University, Tokyo v. 27 (art. 8); ref. 4322] Tosa, Shikoku Island, Kochi Prefecture, Japan. Holotype: ZUMT 2138. Paratypes: ZUMT 2139 (1). •Valid as Sicydium japonicum Tanaka 1909 -- (Okada 1961:688 [ref. 6363]). •Valid as Sicyopterus japonicus (Tanaka 1909) -- (Lindberg & Krasyukova 1975:411 [ref. 7348], Akihito in Masuda et al. 1984:285 [ref. 6441], Kawanabe & Mizuno 1989:638 [ref. 25598], Takahashi 1996:2 [ref. 24363], Kim 1997:446 [ref. 24032], Sato et al. 1998:41 [ref. 24972], Mizuno et al. 1999:12 [ref. 25311], Watson et al. 2000:24 [ref. 25138], Nakabo 2000:1159 [ref. 25182], Matsuura et al. 2000:240 [ref. 26000], Larson & Murdy 2001:3602 [ref. 26293], Sakai et al. 2001:116 [ref. 25693], Kim & Park 2002:370 [ref. 25913], Nakabo 2002:1159 [ref. 26193], Choi et al. 2003:400, 665 [ref. 26218], Yonezawa et al. 2010:257 [ref. 30902], Keith et al. 2015:98 [ref. 34328], Zhang et al. 2016:207 [ref. 34477] as japonica, Maeda & Saeki 2018:260 [ref. 36339], Lord et al. 2020:131 [ref. 37663], Parenti 2021:418 [ref. 38603]). Current status: Valid as Sicyopterus japonicus (Tanaka 1909). Oxudercidae: Sicydiinae. Distribution: Western Pacific: Taiwan to southern Japan. Habitat: freshwater, brackish, marine.