Gephyrocharax machadoi, new species, is described from tributaries of the rio Sepotuba, upper rio Paraguai basin, Mato Grosso state, Brazil. The new species is distinguished from its congeners, except Gephyrocharax major, by presenting two modified scales on the ventral caudal-fin lobe (pouch scales): a larger, sexually dimorphic scale, slightly superior and anterior in position, followed by a smaller, posterior and ventrally placed accessory scale (vs. a single modified pouch scale without ventrally placed accessory scales). Gephyrocharax machadoi differs from G. major by presenting a gap (more conspicuous in mature males than in mature females) between the second and third ventral procurrent caudal-fin rays (vs. second and third ventral procurrent caudal-fin rays near each other or fused distally); premaxilla with tricuspid teeth (vs. tetra- to pentacuspid teeth); and body depth 21.5–25.4% of SL (vs. 25.9–36.8% in SL). Spermiogenesis and spermatozoa morphology are also described.
Eschmeyer, W.N. & Fong, J.D. (2017) Species by family/subfamily in the Catalog of fishes. Electronic Version. Available from: http://researcharchive.calacademy.org/research/ichthyology/catalog/SpeciesByFamily.asp (accessed 25 September 2017)
Fink, W.L. & Weitzman, S.H. (1974) The so-called cheirodontin fishes of Central America with descriptions of two new species (Pisces: Characidae). Smithsonian Contributions to Zoology, 172, 1–46.
Lima, F.C.T. & Ribeiro, A.C. (2011) Continental–scale tectonic controls of biogeography and ecology. In: Albert, J.S. & Reis, R.E. (Eds.), Historical Biogeography of Neotropical Freshwater Fishes. University of California Press, Berkeley, pp 145–164.
Sabaj, M.H. (2016) Standard symbolic codes for institutional resource collections in herpetology and ichthyology: an Online Reference. Version 6.5 (16 August 2016). American Society of Ichthyologists and Herpetologists, Washington, D.C. Electronically accessible. Available from: http://www.asih.org/ (accessed 10 April 2018)
Taylor, W.R. & Van Dyke, G.C. (1985) Revised procedures for staining and clearing small fishes and other vertebrates for bone and cartilage study. Cybium, 9, 107–119.
Thomaz, A.T., Arcila, D., Ortí, G. & Malabarba, L.R. (2015) Molecular phylogeny of the subfamily Stevardiinae Gill, 1858 (Characiformes: Characidae): classification and the evolution of reproductive traits. BMC Evolutionary Biology, 15 (146). [published online]
Vanegas-Ríos, J.A. (2016) Taxonomic review of the Neotropical genus Gephyrocharax Eigenmann, 1912 (Characiformes, Characidae, Stevardiinae). Zootaxa, 4100 (1), 1–92.
Vanegas-Ríos, J.A. (2017) Phylogeny of the Neotropical genus Gephyrocharax (Characiformes: Charcidae: Stevardiinae), with remarks on the tribe Stevardiini. Zoological Journal of the Linnean Society, 182 (4), 808–829.
Vari, R.P. & Harold, A.S. (2001) Neotropical fishes of the genus Creagrutus (Teleostei: Ostariophysi: Characiformes): a phylogenetic study and a revision of the species east of the Andes. Smithsonian Contributions to Zoology, 612, 1–239.
Weitzman, S.H. (1962) The osteology of Brycon meeki, a generalized characid fish, with an osteological definition of the family. Stanford Ichthyological Bulletin, 8 (1), 1–77.