Vertebrates

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.

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.

Based on the examination of the two available paratypes and recently collected material, we present new data and information on the electric knifefish Apteronotus magdalenensis, a species endemic to the río Magdalena-Cauca basin in Colombia. Since Miles' description in 1945, this species was not collected until recent field work at the Torrents of Honda and additional localities. We present data on the external morphology, morphometrics, pigmentation and electric organ discharges (EODs), of A. magdalenensis. We also review its distribution, ecology and conservation status.

Apteronotus eschmeyeri n. sp. is described here from the Magdalena Basin in Colombia and distinguished from congeners by the following combination of features: blotchy coloration on body, clear band from chin to the beginning of dorsal mid-saggital electroreceptororgan, two clear bands surrounding the caudal peduncle in specimens up to 165 mm TL, mouth rictus passing the posterior margin of orbit. The present work demonstrates that the Trans-Andean apteronotids may be more diverse than previously supposed.

A detailed examination of the types of the poorly known nominal gymnotiform apteronotid species Sternarchus mariae Eigenmann & Fisher and Sternarchus jurubidae Fowler, both described from localities in the Trans-Andean region of Colombia, was performed. This investigation resulted in a redescription of the former species, as well as a reevaluation of specific status of the latter. It is concluded that both taxa are valid within the currently recognized genus Apteronotus. The presence of A. eschmeyeri, A. mariae and A. magdalenensis supports the previous hypotheses of the Rio Magdalena Basin as a region of endemism.

Sternarchorhynchus curumim, a new species of tube-snouted ghost knifefish, is described from the main river channel of the Rio Tefé, in the lowland Amazon basin of Brazil. This species is diagnosed from congeners on the basis of body and fin pigmentation, meristic characters such as number of scales above the lateral line at mid-body, and morphometric characters such as relative body proportions. We also provide notes on the ecology and electric organ discharges of this species.Resumo. Sternarchorhynchus curumim, uma espécie nova de ituí, é descrita do canal principal do rio Tefé na bacia Amazônica do Brasil. Esta espécie é diagnosticada dos congêneres com base na pigmentação do corpo e das nadadeiras, caracteres merísticos tal como, o número de escamas acima da linha lateral no centro do corpo, e caracteres morfométricos como as proporções corporais. Nós também, fornecemos notas sobre as descargas do órgão elétrico e ecologia desta espécie.