The former can distinguish it from R. posehensis, and the latter from R. longibarbus. Rectoris mutabilis is similar to R. luxiensis in the shared presence of these two characters, but they differ in the presence or absence of a papillated, triangular patch on the chin. Examination of the type specimens of R. luxiensisshowed that the median plate on the lower lip has a posteromedian patch covered with small densely distributed papillae, and sometimes, a few inconspicuous papillae are scarcely distributed over the slightly sunken area surrounding the posteromedian patch on the median plate of the lower lip (Fig. 3B).