The ability to delimit species and clades is essential to understand their ecology, evolutionary history, and asses their conservation need. Gymnorhamphichthys, known as Sand knifefishes, is a genus of South American weakly electric fishes. The clade has five valid species, most of which have broad geographic distributions with substantial phenotypic variation. These variations resulted in a convoluted taxonomic history, lack of clear diagnostic features and misidentification. Since older taxonomic methodologies failed to distinguish between possible pseudo cryptic species, we expect newer methodologies such as micro-computed tomography, 3D morphometrics and multi loci molecular sequences to allow us to elucidate patterns of diversity within this clade. Data was collected from specimens in museums across North America (ANSP, FMNH, UF, USNM), Brazil (INPA, MZUSP, MNRJ, DZUFMG, LBP, PUC-Minas) and Europe (MHNG). Non-destructive microtomography allowed for character search, osteological description, and species delimitation. Phylogenetic tree was created combining both molecular and morphological matrix following maximum likelihood and posterior Bayesian analysis. Preliminary results support the five valid species already described with external and internal characters, molecular data, and ecological traits. Two possible new species from Guyana and Trombetas region are being evaluated. Results from this research will clarify the alpha taxonomy of Gymnorhamphichthys, addressing a major gap in the field of neotropical freshwater fishes and permit future studies such as how intraspecific variation can be transformed into interspecific differences, evolutionary and biogeography trends of Neotropical freshwater fishes and morphological evolution.