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A recent taxonomic revision of the Neotropical catfish genus Rhamdia (Pisces: Siluriformes: Heptapteridae) reduced a number of described species to synonymy, especially under a broadly circumscribed R. quelen. Evidence is presented here from DNA sequence data, external morphology, and morphometrics that argues for the recognition of R. guatemalensis in Central and northern South America and R. saijaensis and R. cinerascens in the Pacific drainages of Colombia and Ecuador, respectively. The DNA data indicate that all trans-Andean samples form a monophyletic group, within which there are separate clades corresponding to R. laticauda and the synonymized R. guatemalensis, R. saijaensis, and R. cinerascens. The morphometric data substantiate the phylogenetic groupings, and in external morphology, each putative species has diagnostic characters. Rhamdia guatemalensis is characterized by insertion of the adipose fin closer to the dorsal fin than to the caudal fin and presence of a conspicuous lateral longitudinal dark band; R. saijaensis is characterized by a small head with head length 20.8–23.4% of standard length and by lacking a lateral longitudinal band; and R. cinerascens is characterized by a large head with head length 25.8–30.1% of standard length, base of the adipose fin 30.3–33.3% of standard length, outer mental barbels extending to the base of the pectoral rays, and presence of a faint lateral longitudinal band. The external morphological differences and phylogenetic relationships indicate that these groups are both recognizable and represent independent lineages, which argue for their recognition as species.

The phylogenetic relationships of the poorly known nominal heptapterid genera Nemuroglanis, Imparales, and Medemichthys, and the validity of their species, are examined on the basis of type- and recently discovered material. These genera are known from the Amazon River basin of Brazil, Ecuador, Peru, and Venezuela, and the Orinoco River basin of Venezuela. Two species were described in Nemuroglanis, Nemuroglanis lanceolatus, its type species, from the Amazon River, and Nemuroglanis pauciradiatus, from the Orinoco and Negro River basins. Imparales includes its type species, Imparales mariai, from the Orinoco River basin, and Imparales panamensis, from Panama. Medemichthys, also known from Orinoco River basin, is monotypic, with Medemichthys guayaberensis as its type species. Based on the study of morphological characters, we conclude that (1) N. lanceolatus, N. pauciradiatus, and I. mariai constitute a monophyletic group within the Heptapteridae, but I. panamensis is not a member of this clade and...

Heptapterus collettii Steindachner, 1881, a catfish described from La Plata basin in South America, has a puzzling set of characters for Neotropical siluriforms. Examination of one syntype shows that H. collettii does not belong to Heptapteridae or any other Neotropical family but rather to Olyra, a genus of Bagridae endemic to South Asia. Thus, it should be referred to as Olyra collettii. The species has nasal barbels on the posterior nares (shared with various Old-World catfish taxa), a wide separation between the anal and urogenital openings (shared with a large subgroup of Bagridae) and a unique structure of the first lateral-line ossicle (shared with species of Olyra). The species is similar to Olyra longicaudata, although there are significant morphometric and meristic differences. Current problems in the taxonomy of Olyra prevent conclusive resolution of the identity of O. collettii. The presence of a species of Olyra in South America is unlikely, and we consider this to be a result of mis...

Pimelodella spelaea, new species, is described from a subterranean stream tributary to the Sao Bernardo River inside the Sao Bernardo Cave, in the Sao Domingos karst area, upper Tocantins River basin, central Brazil. The new species can be distinguished from its epigean (surface) congeners by derived troglomorphic features such as smaller eyes and fainter coloration, which are nevertheless less reduced than in the other known troglobitic (exclusively subterranean) species, Pimelodella kronei, from southeast Brazil. Ecological data such as habitat characteristics, population data based on mark-recapture techniques, and distributions of frequencies of standard length, weight, and condition factor, were obtained during the dry season of 2000 (May to September). A relatively high population density (about one individual per m−2) was recorded for the accessible habitat, which is probably much lower in the nonaccessible, phreatic area of distribution. The low condition factor recorded for P. spelaea, w...