Re-validation of Otocinclus arnoldi Regan and reappraisal of Otocinclus phylogeny (Siluriformes: Loricariidae) Author A, Pablo Lehmann Author Mayer, Fernanda Author Reis, Roberto E. text Neotropical Ichthyology 2010 8 1 57 68 journal article 1982-0224 Otocinclus flexilis Cope, 1894 Fig. 2 Otocinclus flexilis Cope, 1894: 97 , pl. 8, fig. 13. Type locality: rio Jacuhy , Rio Grande do Sul [rio Jacuí, Brazil ]. Lectotype : ANSP 21756 , 40.0 mm SL, designated by Schaefer (1997: 53) . Otocinclus fimbriatus Cope, 1894: 98 , pl. 9, fig. 16. Type locality: rio Jacuhy , Rio Grande do Sul [rio Jacuí, Brazil ]. Syntypes : ANSP 212752 (4) andANSP 21585-97 (14). Diagnosis. Otocinclus flexilis is distinguished from all other Otocinclus (except for O . xakriaba , O . affinis , O . hasemani , O . arnoldi , and O . mimulus ) by possessing an iris operculum and (except for O . xakriaba , O . arnoldi , and O . mimulus ) by having a lateral trunk coloration consisting of a series of 3-6 diffuse pigment blotches ( Fig. 2 ). An inconspicuous and not elevated patch of 0-10 (mode = 0, mean = 3.0) enlarged odontodes on the postero-dorsal parieto-supraoccipital tip, the pectoral skeleton with closed arrector fossae , and the presence of a triangular pigment mark at the dorsal-fin base distinguishes O . flexilis from O . xakriaba , which possesses an elevated patch of enlarged odontodes on the parietosupraoccipital, has an open arrector fossae , and lacks the dorsal-fin mark. From O . arnoldi and O . mimulus it is easily distinguished by having six branched pectoral-fin rays ( vs . five branched rays) and few (0-10, mode = 0, mean = 3.0) not elevated enlarged odontodes on the parieto-supraoccipital tip ( vs . 2-23, mode = 7, mean = 8.3) not elevated enlarged odontodes in O . arnoldi and 5-14, mode = 7, mean = 8.4 conspicuously elevated odontodes in O . mimulus ). Distribution. Otocinclus flexilis is restricted to the laguna dos Patos drainage basin ( Fig. 5 ).