Aim  To provide an objective geographic framework displaying the distribution patterns of freshwater fishes from Argentina. Location  Argentina, southern South America. Methods  Parsimony analysis of endemicity (PAE) and similarity and cluster analyses were applied to presence and absence data on 440 fish species from 52 localities in Argentina. Both 50% majority consensus and strict consensus analyses were undertaken in the first case, and the Jaccard similarity index was used in the second. Results  Five ichthyogeographic provinces are described based on a PAE of the 52 localities. A cluster analysis provided similar results. Main conclusions  The following zoogeographic provinces are proposed for Argentine freshwater fish fauna following the International Code of Area Nomenclature: Andean Cuyan, Patagonian, Aymaran, Great Rivers and Pampean. The former two are placed within the Andean Subregion of the Austral Region, and the latter three within the Neotropical Subregion of the Holotropical Region. These provinces, based on results coinciding with PAE and cluster analysis, represent the first classification of Argentine provinces based on objective methods. Some small regions of endemism and some localities remain separated from the proposed regions. The new scheme includes valuable empirical information from previous schemes, and is in agreement with ecological zones and other environmental arrangements proposed earlier.

Rhamdella cainguae, a new species of the family Heptapteridae is described from the Arroyo Cuña-Pirú, a tributary of the Río Paraná, in the subtropical forest of Misiones, northeastern Argentina. The presence of a large differentiated ovoid area on the supraorbital laterosensory canal along the frontal-sphenotic boundary, delimited by the slender dorsal walls of the bones, and with no foramen for a laterosensory branch, is an autapomorphy for R. cainguae. A detailed description of the skeleton and laterosensory system of R. cainguae is provided. The genus Rhamdella is rediagnosed on the basis of three autapomorphies: a very large opening in the frontal for the exit of the s6 (epiphyseal) branch of the supraorbital laterosensory canal (reversed in R. rusbyi), a large optic foramen, and a dark stripe along the lateral surface of the body (reversed in R. rusbyi). Rhamdella is considered to be the sister group of a large heptapterid clade composed of the Nemuroglanis sub-clade plus the genera Brachyglanis, Gladioglanis, Leptorhamdia, and Myoglanis. Rhamdella is herein restricted to five valid species: R. aymarae, R. cainguae, R. eriarcha, R. longiuscula, and R. rusbyi. A sister group relationship between R. aymarae and R. rusbyi is supported by three synapomorphies. Rhamdella cainguae shares 12 apomorphic features with R. eriarcha and R. longiuscula.

cny m .unlp .edu .ar.Astyanax tumbayaensis, a new species from northwestern Argentina highlands (Characiformes: Characidae) with a key to the Argentinean species of the genus and comments on their distribution. -A new species of the characid genus Astyanax is described from a man-made small channel connected with the Rio Grande basin, in Jujuy Province, northwestern Argentina. This species can be distinguished from its congeners by the following combination of characters: body relatively high (39.2-45.3% SL); head short and heavy (24.0-26.7% SL); snout very short (16.1-20.8% HL); eye small (28.9-35.0% HL); interorbital very wide (38.8-44.1% HL); mouth sub-superior; maxilla short with 1-2 teeth; iii-v, 19-22 anal fin rays; 33-36 perforated scales on the lateral line, and a distinctive color pattern, consisting in a reticulated body, with dorsal, pelvic, anal, and caudal fins with dark margins. A very narrow lateral dark stripe ending in a caudal spot, and one large vertically elongated humeral spot. In addition the males of Astyanax tumbayaensis have bony hooks in the dorsal, pelvic, anal and caudal fins. A key for Argentinean species of Astyanax is provided. The primary traits of the distribution of species in the country are discussed, with reference to the main basins and some zoogeographically important localities.

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Rineloricaria misionera is a new species from the Paraná and Uruguay River basins, Misiones, Argentina. The new species is distinguished from all others in the genus by the following combination of characters: anterior abdomen covered by plates, except for the area corresponding to the pectoral girdle, which usually lacks plates, when present in this region, plates are relatively small and few; posterior abdomen with a well-developed preanal plate, bordered anteriorly by a series of 3–5 usually polygonal plates; premaxillary and dentary teeth with asymmetric cusps; uppermost caudal ray not prolonged in a filament; and snout tip with an oval naked area not reaching the last pore of the infraorbital sensory canal.

The fish fauna and its relationships with physiography and climate were studied in northwestern Argentina from 21°30¢ S to 26°30¢ S and 63°30¢ W to 65°50¢ W, an area about 10,276 km 2 . Along a southeastnorthwest gradient, the Chaco forest at low altitudes gives way to the Yungas cloud forest in highlands, and then, to an increasing desertic landscape, with xerophytic vegetation and scarce rainfall along the Grande River. Finally, extreme desert conditions prevail in the most northern part at the Puna plateau. Water chemistry was sampled from sites from 400 to over 3800 m a.s.l. In all 3278 fish specimens of 52 species were collected. Previous lists included 84 species. Only 19 were shared, meaning that 40 species are new for the area and/or particular localities, including 7 reports from Aguas Calientes. These results increase by one third the number of species in northwestern Argentina. The fish fauna was represented by eurytopic species of Paranensean genera as Astyanax, Bryconamericus and other characoids, mixed with locally distributed siluriforms. Under extreme climatic conditions, species of Trichomycterus predominate. Species assemblages show a combination of a large number of species typical of, sometimes endemic to or rather abundant in, the area, combined with a few species of Paranensean character. Fish assemblages were clearly defined by faunistic composition and distribution related with physiography and climate traits. A significant negative correlation is observed between both species number and abundance, and increasing altitude, and positive relationships exist with mean annual temperature and other climate traits. Diversity values (Shannon index) agree with the described pattern of increasing impoverishment of the fish fauna of northwestern Argentina, along gradients of increasing altitude and dryness and decreasing temperature.

A new species of the hypoptopomatine genus Hisonotus (Loricariidae) is described from a small tributary of the upper río Uruguay basin near the border between Uruguay and Brazil. The new species can be distinguished from all other congeners by the following combination of characters: (1) presence of serrae along distal two thirds of posterior margin of pectoral-fin spine (versus serrae absent, posterior margin smooth); (2) odontodes along anterior margin of snout biserially arranged, dorsad and ventrad series separated by narrow odontode-free area covered by pad of soft tissue; (3) caudal peduncle short (27-34% SL, versus Ͼ 34% SL) and deep (13-15 % SL, versus Ͻ 13% SL); (4) eye large (15-19% HL, versus Ͻ 13% HL); and (5) caudal-fin pigmentation, when well defined, dark brown with a pair of whitish blotches on upper and lower lobes. The significance of the distribution of the new species is discussed relative to the degree of endemism of other fish groups in the Uruguay basin. RESUMENUna nueva especie de Hypoptopomatinae del género Hisonotus (Loricariidae) es descripta para un pequeño tributario del río Uruguay superior, cerca del límite entre Uruguay y Brasil. La nueva especie puede distinguirse de todas las otras especies nominales del género por la siguiente combinación de caracteres: (1) presencia de sierra a lo largo del margen posterior de los dos tercios distales de la espina pectoral (versus margen posterior liso), (2) odontodes del margen anterior del hocico ordenados biserialmente, las series dorsal y ventral separadas por una banda angosta libre de odontodes, cubierta por tejido blando; (3) pedúnculo caudal 2 NO. 3333 AMERICAN MUSEUM NOVITATES corto (27-34 % LE, versus usualmente Ͼ 34) y alto (13-15 % LE, versus usualmente Ͻ 13); (4) ojo grande (15-19 % in HL, versus usualmente Ͻ 13), y (5) patrón de coloración de la aleta caudal, cuando se encuentra bien definido, marrón oscuro, con un par de manchas blanquecinas sobre los lóbulos superior e inferior de la aleta. La distribución geográfica de la nueva especie es discutida en relación al grado de endemismo registrado en otros grupos de peces de la cuenca del río Uruguay.

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