Carlos David de Santana

The South American Electric Fish Genus Platyurosternarchus (Gymnotiformes: Apteronotidae)

Abstract The electric fish genus Platyurosternarchus, family Apteronotidae, is reviewed based on both external morphology and osteology. Synapomorphies for Platyurosternarchus are identified, the genus is diagnosed, and a key to the species is provided. Platyurosternarchus crypticus, a new species, is described from the upper reaches of the Rio Branco in the northern portions of the Amazon basin. Platyurosternarchus macrostoma from the Amazonas, Orinoco, and Essequibo River basins is redescribed. The species differ in the form of the laterosensory canal segment in the soft tissues of the ventral portion of the head and within the preopercle, the posterior extent of the mid-dorsal electroreceptive filament, and the morphology of the first and fourth branchiostegal rays.

New Rheophilic Species of Electric Knifefish from the Rapids and Waterfalls of the Lower Rio Xingu, Brazil (Gymnotiformes: Apteronotidae)

Abstract Sternarchogiton zuanoni, a new species of electric knifefish, is described from the rapids and waterfalls of Cachoeira de Kaituká along the Rio Xingu at Altamira, Pará, Brazil. The new species is diagnosable from congeners by a unique combination of morphometric and meristic features, details of pigmentation, the pattern of dentition on the dentary, the possession of an edentulous premaxilla, and an unelaborated lower lip. The description of S. zuanoni brings the number of species in the genus to five. The presence of S. labiatus in the Río Orinoco basin is documented and a key to the species of the genus is provided.

The Untold Story of the Caudal Skeleton in the Electric Eel (Ostariophysi: Gymnotiformes: Electrophorus)

Alternative hypotheses had been advanced as to the components forming the elongate fin coursing along the ventral margin of much of the body and tail from behind the abdominal region to the posterior margin of the tail in the Electric Eel, Electrophorus electricus. Although the original species description indicated that this fin was a composite of the caudal fin plus the elongate anal fin characteristic of other genera of the Gymnotiformes, subsequent researchers proposed that the posterior region of the fin was formed by the extension of the anal fin posteriorly to the tip of the tail, thereby forming a “false caudal fin.” Examination of ontogenetic series of the genus reveal that Electrophorus possesses a true caudal fin formed of a terminal centrum, hypural plate and a low number of caudal-fin rays. The confluence of the two fins is proposed as an additional autapomorphy for the genus. Under all alternative proposed hypotheses of relationships within the order Gymnotiformes, the presence of a caudal fin in Electrophorus optimized as being independent of the occurence of the morphologically equivalent structure in the Apteronotidae. Possible functional advantages to the presence of a caudal fin in the genus are discussed.

The South American Electric Glass Knifefish Genus Distocyclus (Gymnotiformes: Sternopygidae): Redefinition and Revision

Electric glass knifefishes of the genus Distocyclus, family Sternopygidae, are reviewed. Features previously utilized to diagnose Distocyclus were found uninformative as to whether the two species originally assigned to the genus are sister taxa. Distocyclus goajira was found to lack the derived features present in the type-species of the genus, D. conirostris and instead shares derived features with Archolaemus, Eigenmannia, and/or Japigny; however, the relationships of Distocyclus goajira among those genera cannot be resolved. In light of this evidence, Distocyclus is restricted to its type species, D. conirostris, which is defined on a series of derived characters, and D. goajira is assigned as incertae sedis in the Eigenmanniinae under a new combination of “Eigenmannia” goajira. Distocyclus conirostris is redescribed on the basis of multiple samples from across the Amazon, Essequibo, and Orinoco river basins. Os peixes elétricos do gênero Distocyclus, família Sternopygidae, são revisados. Os caracteres diagnósticos previamente propostos para Distocyclus se mostraram não informativos em relação as duas espécies originalmente alocadas neste gênero como espécies irmãs. Distocyclus goajira não apresenta os caracteres derivados presentes na espécie tipo do gênero, D. conirostris, e ainda compartilha caracteres derivados em diferentes combinações com Archolaemus, Eigenmannia e Japigny. Baseado na presente evidência, Distocyclus é restringido a sua espécie tipo, D. conirostris que é definido por uma série de caracteres derivados e D. goajira é considerada incertae sedis em Eigenmanniinae, sob a nova combinação de “Eigenmannia” goajira. Distocyclus conirostris é redescrito com base em várias amostras ao longo das bacias dos rios Amazonas, Essequibo e Orinoco.

Phylogenetic Systematics, Biogeography, and Ecology of the Electric Fish Genus Brachyhypopomus (Ostariophysi: Gymnotiformes)

A species-level phylogenetic reconstruction of the Neotropical bluntnose knifefish genus Brachyhypopomus (Gymnotiformes, Hypopomidae) is presented, based on 60 morphological characters, approximately 1100 base pairs of the mitochondrial cytb gene, and approximately 1000 base pairs of the nuclear rag2 gene. The phylogeny includes 28 species of Brachyhypopomus and nine outgroup species from nine other gymnotiform genera, including seven in the superfamily Rhamphichthyoidea (Hypopomidae and Rhamphichthyidae). Parsimony and Bayesian total evidence phylogenetic analyses confirm the monophyly of the genus, and identify nine robust species groups. Homoplastic osteological characters associated with diminutive body size and occurrence in small stream habitats, including loss of squamation and simplifications of the skeleton, appear to mislead a phylogenetic analysis based on morphological characters alone–resulting in the incorrect placing of Microsternarchus + Racenisia in a position deeply nested within Brachyhypopomus. Consideration of geographical distribution in light of the total evidence phylogeny indicates an origin for Brachyhypopomus in Greater Amazonia (the superbasin comprising the Amazon, Orinoco and major Guiana drainages), with subsequent dispersal and vicariance in peripheral basins, including the La Plata, the São Francisco, and trans-Andean basins of northwest South America and Central America. The ancestral habitat of Brachyhypopomus likely resembled the normoxic, low-conductivity terra firme stream system occupied by many extant species, and the genus has subsequently occupied a wide range of terra firme and floodplain habitats including low- and high-conductivity systems, and normoxic and hypoxic systems. Adaptations for impedance matching to high conductivity, and/or for air breathing in hypoxic systems have attended these habitat transitions. Several species of Brachyhypopomus are eurytopic with respect to habitat occupancy and these generally exhibit wider geographical ranges than stenotopic species.

New Species of Adontosternarchus (Gymnotiformes, Apteronotidae) from the Rio Purus Basin, Brazil

A new species of the genus Adontosternarchus (Gymnotiformes, Apteronotidae) is described from samples collected during high water periods in a relatively restricted area within the Rio Purus basin, Amazonas, Brazil. Adontosternarchus duartei differs from congeners in a series of details of pigmentation, meristics, and morphometrics and represents the sixth species in the genus. A key to the species of Adontosternarchus is provided.

A Review of the South American Electric Fish Genus Porotergus (Gymnotiformes: Apteronotidae) with the Description of a New Species

Abstract The species currently assigned to the South American electric fish genus Porotergus are reviewed. Porotergus duende, a new species, is described from the lowland western Amazon basin in Brazil and Peru. Porotergus gimbeli from the lowland Amazon basin in Brazil and Peru, and P. gymnotus from the Essequibo drainage of Guyana are redescribed. Porotergus duende and P. gimbeli are restricted to deep channel habitats. Porotergus gymnotus occurs in shallow rivers. Notes on the ecology and electric organ discharge of P. duende and P. gimbeli are presented. A key to the members of the genus is provided.

A New Species of the Electric Fish Genus Hypopygus (Gymnotiformes: Hypopomidae) from the Lower Amazon Basin, Brazil

Hypopygus benoneae, new species, is described from streams in the lower Rio Anapu, in the eastern portion of the Amazon basin, Brazil. The new species is diagnosed from all congeners by a unique set of characters, including the absence of the sixth infraorbital bone and 115–134 total anal-fin rays. Hypopygus benoneae, new species, is a member of a clade also comprising H. hoedemani, H. lepturus, and H. minissimus. The description of H. benoneae, new species, brings the number of species in Hypopygus to nine. A dichotomous key to the species of Hypopygus is provided. Hypopygus benoneae, nova espécie, é descrita para igarapés do baixo Rio Anapu, na porção oriental da bacia Amazônica, Brasil. A nova espécie é diagnosticada de todos os congêneres por uma combinação única de caracteres, tais como a ausência do sexto osso infraorbital e o número total de raios da nadadeira anal 115–134. Hypopygus benoneae, nova espécie, é um membro do clado que também inclui H. hoedemani, H. lepturus, and H. minissimus. A descrição de H. benoneae, nova espécie, eleva o número de espécies em Hypopygus para nove. Uma chave dicotômica para as espécies de Hypopygus é fornecida.

A New Species of the Glass Electric Knifefish Genus Eigenmannia Jordan and Evermann (Teleostei: Gymnotiformes: Sternopygidae) from Río Tuíra Basin, Panama

A new species of Eigenmannia is described from the Río Pucuro, Río Tuíra basin, Panama. It is diagnosed from all congeners by the position of the mouth, the color pattern, the number of anal-fin rays, the number of scales on lateral line, the number of scales rows above the lateral line, the number and arrangement of teeth on the dentary, the number of precaudal vertebrae, the relative depth of the posterodorsal expansion on infraorbitals 1+2, and the relative size of coronomeckelian bone. The new species is the first Eigenmannia described from Central American drainages, and the northernmost species of the genus. Una nueva especie de Eigenmannia es descrita del río Pucuro, que pertenece a la cuenca del Río Tuíra, Panamá. Esta diagnosticada de las demás especies del género por la posición de la boca, el padrón de coloración, el número de radios de la aleta anal, el número de escamas de la línea lateral, el número de hileras de escamas arriba de la línea lateral, el número y disposición de los dientes en el hueso dentario, el número de vertebras pre-caudales, el tamaño relativo de la expansión postero-dorsal del hueso infraorbital 1+2 y el tamaño relativo del hueso corono-meckeliano. Esta nueva especie es la primera Eigenmannia descrita de las cuencas de América Central y además es la especie con la distribución más boreal del género.

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.