In the present work, we integrated genetics with classical morphometry in order to redefine the enigmatic Hypostomus plecostomus. The three rediscovered syntypes were compared to hundreds of Hypostomus specimens from the Guianas representing 15 nominal species by means of classical multivariate morphometric analyses. Most of this material was collected by the authors and collaborators during the past 15 years (see Le Bail et al., 2012; Mol et al., 2012). A significant part of the specimens was specifically sampled for diverse genetic studies, including an allozyme analysis that was conducted at the MHNG. The taxonomy of H.plecostomus is here accordingly redefined and a complementary description provided. The taxonomic status of several of the 21 nominal Guianese species of Hypostomus occurring from the Oyapock to the Essequibo Rivers is also revised to establish
a list of presumably valid species of the region.