Eigenmannia trilineata López and Castello, 1966 (Sternopygidae) was described from the Río de La Plata basin and subsequently cited from most South American river basins. Questions about the limits of this species raise the possibility of the occurrence of undescribed species misidentified as E. trilineata. Herein we propose the Eigenmannia trilineata species group for species that share the presence of the superior medial stripe on the flank. This group comprises: Eigenmannia antonioi sp. nov., from the Rio Anapu, Rio Amazonas basin; Eigenmannia desantanai sp. nov., from the Rio Cuiabá, Rio Paraguay basin; Eigenmannia guairaca sp. nov., from the Riacho Água do Ó, upper Rio Paraná basin; Eigenmannia matintapereira sp. nov., from the Rio Uneiuxi and Rio Urubaxi, Rio Negro basin; Eigenmannia microstoma (Reinhardt, 1852), from the Rio São Francisco basin; Eigenmannia muirapinima sp. nov., from small tributaries of the Rio Amazonas; Eigenmannia pavulagem sp. nov., from the tributaries of Rio Capim, Rio Guamá basin; E. trilineata, from the lower Rio Paraná basin and Río de La Plata basin; Eigenmannia vicentespelaea Triques, 1996, from São Vicente I and II caves, Rio Tocantins basin; and Eigenmannia waiwai sp. nov., from the Rio Trombetas basin. These species can be distinguished from each other by unique sets of meristics, morphometrics, osteological and colour pattern features. © 2015 The Linnean Society of London

Is there only one electric eel species? For two and a half centuries since its description by Linnaeus, Electrophorus electricus has captivated humankind by its capacity to generate strong electric discharges. Despite the importance of Electrophorus in multiple fields of science, the possibility of additional species-level diversity in the genus, which could also reveal a hidden variety of substances and bioelectrogenic functions, has hitherto not been explored. Here, based on overwhelming patterns of genetic, morphological, and ecological data, we reject the hypothesis of a single species broadly distributed throughout Greater Amazonia. Our analyses readily identify three major lineages that diverged during the Miocene and Pliocene—two of which warrant recognition as new species. For one of the new species, we recorded a discharge of 860 V, well above 650 V previously cited for Electrophorus, making it the strongest living bioelectricity generator.

A new species of Eigenmannia is described from the rio Mutum, tributary of upper rio Juruena, rio Tapajós basin, Comodoro, Mato Grosso, Brazil. The new species is distinguished from all congeners by coloration pattern, position of the mouth, number of scales rows above lateral line, number of premaxillary and dentary teeth, number of precaudal vertebrae, orbital diameter, mouth width, relative depth of posterodorsal expansion on infraorbitals 1+2 and relative size of coronomeckelian bone. Comments on potentially useful characters in phylogenetic studies derived from musculature, discussion on Eigenmannia species-group and the first dichotomous key for Eigenmannia are provided.

Eigenmannia species are widely distributed in the Neotropics, with eight valid species currently recognized. Populations of Eigenmannia from three locations in the eastern Amazon were investigated using cytogenetic and morphological techniques, revealing two taxa designated here as Eigenmannia sp. "A" and Eigenmannia sp. "B". The species differ in three morphometric characters, two meristic characters, and one osteological character. Eigenmannia sp. "A" presents 2n = 34 (22 m/sm+12 st/a) and Eigenmannia sp. "B" presents 2n = 38 (14 m/sm+24st/a) and simple differentiated sex chromosomes of the type XX/XY. In both species the Constitutive Heterochromatin (CH) rich in A-T bases is distributed in the centromeric region of all chromosomes. Eigenmannia sp. "B" also presents CH blocks in the interstitial region of chromosome pairs 8, 9 and X which are positively stained with CMA3, indicating G-C rich regions. The NOR is located on the short arm of chromosome pair 17 of Eigenmannia sp. "A" and on the short arm of pair 14 of Eigenmannia sp. "B". FISH with rDNA probes hybridized to different-sized regions between homologs, suggesting heteromorphism. The differentiation of the X chromosome in Eigenmannia sp. "B" could be the result of amplification of repetitive DNA sequences.

A new species of the Eigenmannia trilineata species-group is described from the rio São Francisco basin, Brazil. It is distinguished from closely related species by a unique set of characters, including a subterminal mouth, the presence of ii,13-14 pectoral-fin rays, a coronomeckelian bone that is 30% the length of Meckel's cartilage, the specific pattern of the dentition of the premaxilla and dentary, and the more anterior origin of the superior midlateral stripe. Comments on species of the E. trilineata species-group are presented.

A new species of the Eigenmannia trilineata species group is described from the río Orinoco basin, Venezuela. The new species is distinguished from congeners by a unique set of characters including an ossified basibranchial 1; 198-217 anal-fin rays; suborbital depth, 21.3-26.1% HL; length of anterodorsal process of maxilla equal to the width of the posterior nostril; premaxilla with 17 teeth distributed in three rows; hyaline pectoral and anal fins; and number of scale series above lateral line, 9-10. It raises the number of species allocated to the Eigenmannia trilineata species group to 13 and the number of species within the genus to 18.Keywords: Biodiversity, Electric-fishes, Taxonomy, Tuvira.Se describe una nueva especie del grupo Eigenmannia trilineata de la cuenca del río Orinoco, Venezuela. La nueva especie se distingue de sus congéneres por una combinación única de caracteres, incluyendo el basibranquial 1 osificado; número de radios de la anal, 198-217; profundidad del suborbital, 21.3-26.1% HL; longitud del proceso anterodorsal de la maxila igual al ancho de la narina posterior; 17 dientes premaxilares distribuidos en tres hileras; aletas pectoral y anal hialinas; y 9-10 hileras de escamas sobre la serie de la línea lateral. La presente contribución eleva el número de especies del grupo Eigenmannia trilineata a 13, y a 18 aquellas dentro del género.

A new species of Eigenmannia is described from the Río Ventuari, Río Orinoco basin, Venezuela. It is distinguished from congeners by the presence of a bony dorsolateral flange on the dentary, the presence of teeth attached along a bony dorsolateral flange, and by the first premaxillary teeth attached to the anteroventral margin of the premaxilla. It is further distinguished from all remain congeners by a combination of characters, including a subterminal mouth, 99–107 scales along the lateral line until the end of the anal fin, and ii, 16–17 pectoral-fin rays.

A new species of Farlowella is described from eighteen specimens collected in the upper rio Xingu basin, Mato Grosso State, Brazil. The new species is a member of the Farlowella nattereri species-group and can be distinguished from other members of the group, with exception of Farlowella jauruensis, by exhibiting a proportionally shorter snout. The new species is distinguished from F. jauruensis by differences on the cleithrum and plate morphology, by counts of pelvic and caudal-fin rays, and by the color pattern of the snout. The discovery of new lots of F. jauruensis, a species so far known only from the holotype, is also herein reported. This discovery represents a considerable expansion of the geographic distribution and of the number of known specimens of F. jauruensis. Uma nova espécie de Farlowella é descrita de dezoito espécimes da bacia do alto rio Xingu, estado do Mato Grosso, Brasil. A nova espécie é membro do grupo de espécies da Farlowella nattereri, e é diagnosticada de outros membros deste grupo, com exceção de Farlowella jauruensis, por apresentar um focinho proporcionalmente mais curto. A nova espécie se diferencia de F. jauruensis por diferenças morfológicas do cleitro e de placas, pelas contagens de raios da nadadeira pélvica e caudal, e pelo padrão de colorido do focinho. A descoberta de novos lotes de F. jauruensis, uma espécie até então conhecida apenas pelo holótipo, também é aqui reportada. Esta descoberta representa uma expansão considerável da distribuição geográfica e do número de espécimes conhecidos de F. jauruensis.