arnoldi, Otocinclus Regan [C. T.] 1909:234 [Annals and Magazine of Natural History (Series 8) v. 3 (no. 14); ref. 14416] "La Plata" [?Rio de la Plata], South America. Holotype (unique): BMNH 1908.12.5.13. Type catalog: Ferraris 2007:271 [ref. 29155]. •Synonym of Macrotocinclus flexilis (Cope 1894) -- (Isbrücker 2001:30 [ref. 25653], Isbrücker 2002:23 [ref. 27178], Ferraris 2007:271 [ref. 29155]). •Synonym of Otocinclus flexilis Cope 1894 -- (Aquino 1996:13 [ref. 22664], Schaefer 1997:49 [ref. 23213], Schaefer in Reis et al. 2003:324 [ref. 27061], Carvalho & Reis 2009:2 [ref. 30193]). •Valid as Otocinclus arnoldi Regan 1909 -- (Isbrücker 1980:81 [ref. 2303], Burgess 1989:438 [ref. 12860], Lehmann A. et al. 2010:60 [ref. 30756], Koerber 2011:5 [ref. 31122], Koerber 2014:8 [ref. 33621], Litz & Koerber 2014:24 [ref. 33622], Mirande & Koerber 2015:40 [ref. 35117], Ribeiro & Lehmann A. 2016:240 [ref. 34636], Bertaco et al. 2016:419 [ref. 34561], Nión et al. 2016:31 [ref. 35565], Koerber et al. 2017:59 [ref. 35267], Delapieve et al. 2018:23 [ref. 35713], Loureiro et al. 2023:117 [ref. 40506]). Current status: Valid as Otocinclus arnoldi Regan 1909. Loricariidae: Hypoptopomatinae. Distribution: South America: lower Paraná, Uruguai and de La Plata River basins (Brazil, Uruguay and Argentina). Habitat: freshwater.