Isbrueckerichthys epakmos, new species, is described from the tributaries of the rio Juquiá, rio Ribeira de Iguape basin, São Paulo State, Brazil. The new species displays a unique sexual dimorphism. Mature males are distinguished from its congeners by having a well-developed soft fleshy area and a clump of hypertrophied short odontodes directed forward or slightly upward on anterior portion of snout. It is compared with I. duseni and I. alipionis, which occurs sympatrically in the rio Ribeira de Iguape drainage. A key to the species of Isbrueckerichthys is provided.
Atlantic Forest; systematics; Isbrueckerichthys duseni; Isbrueckerichthys alipionis