A new species of the electric fish Microsternarchus Fernández-Yépez 1968 (Gymnotiformes: Hypopomidae) from the lower Amazon basin, Brazil.

A new species of Microsternarchus is described from clear water streams in the lower Rio Amazonas basin, Brazil, increasing the known species in the genus to three. The new species is distinguished from congeners by a unique set of characters including an elongated caudal filament (35.1-36.

Integrative taxonomy reveals a new species of the glass knifefish genus Eigenmannia Jordan & Evermann, 1896 (Teleostei: Gymnotiformes: Sternopygidae) from the Rio Branco basin, Brazil.

A new species of Eigenmannia is described from the Rio Branco basin, Roraima, Brazil, based on morphological and molecular datasets. It is distinguished from all congeners by the following combination of characters: lateral line stripe extending from first perforated lateral line scale to distal portion of caudal filament, presence of superior midlateral stripe with origin posterior to end of body cavity anal-fin hyaline, caudal filament corresponding to 15.2%-43.

A new species of sexually dimorphic and rheophilic ghost knifefish (Apteronotidae: Gymnotiformes) from the Amazon basin.

A new species of ghost knifefish, Apteronotus, is described from high-energy environments in the Rios Mapuera and Trombetas (at Cachoeira Porteira waterfalls), Brazil. X-ray microcomputed tomography (μCT scan) was used to access the internal anatomy of the type series. The new species is distinguished from all congeners by the anteriormost position of the anus, with its posterior margin extending less than one eye diameter beyond the vertical through the caudal limit of the posterior nostril, the low number of anal-fin rays (117-125) and the reduced number of branchiostegal rays (three).

New species of glass knifefish genus Eigenmannia (Gymnotiformes: Sternopygidae) with comments on the morphology and function of the enlarged cephalic lateral-line canals of Sternopygidae.

A new species of Eigenmannia is described from the Rio Paraná (the Grande, Paranapanema and Tietê basins). This new species is distinguished from all congeners by colouration pattern, position of the mouth, relative depth of posterodorsal expansion on infraorbitals 1 + 2, number of teeth, osteological features, number of rows of scales above lateral line (LL) and morphometric data. Comments on the widened cephalic lateral-line canals of Sternopygidae and a dichotomous key to the species of Eigenmannia from the Rio Paraná Basin are provided.

Anatomical, taxonomic, and phylogenetic reappraisal of a poorly known ghost knifefish, Tembeassu marauna (Ostariophysi: Gymnotiformes), using X-ray microcomputed tomography.

A detailed osteological study of the poorly known and critical endangered ghost knifefish, Tembeassu marauna, from the rio Paraná, Brazil, was conducted using X-ray microcomputed tomography (μCT scan). A redescription of the external anatomy was performed, including the unusual presence of a rostral patch of extra teeth on the region of the upper lip anterior to the premaxilla and the prominent anterior fleshy expansions in both upper and lower lips. The newly surveyed characters were included and analyzed in light of a recent morphological data matrix for Gymnotiformes.

A new species of Eigenmannia Jordan & Evermann (Gymnotiformes: Sternopygidae) from rio Tapajós, Brazil, with discussion on its species group and the myology within Eigenmanniinae.

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.

A new species of Eigenmannia Jordan Evermann (Teleostei: Gymnotiformes: Sternopygidae) from Río Ventuari, Venezuela.

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.

Eigenmannia besouro, a new species of the Eigenmannia trilineata species-group (Gymnotiformes: Sternopygidae) from the rio São Francisco basin, northeastern Brazil.

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.