The genus Rineloricaria is a Neotropical freshwater fish group with a long and problematic taxonomic history, attributed to the large number of species and the pronounced similarity among them. In the present work, taxonomic information and different molecular approaches were used to identify species boundaries and characterize independent evolutionary units. We analyzed 228 samples assembled in 53 distinct morphospecies. A general mixed yule-coalescent (GMYC) analysis indicated the existence of 70 entities, while BOLD system analyses showed the existence of 56 distinct BINs. When we used a new proposed integrative taxonomy approach, mixing the results obtained by each analysis, we identified 73 OTUs. We suggest that Rineloricaria probably has some complexity in the known species and several species not formally described yet. Our data suggested that other hyperdiverse fish groups with wide distributions can be further split into many new evolutionary taxonomic units.

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Recent investigations in the upper Río Huallaga in Peru revealed the presence of an intriguing species of the Loricariinae. To characterize and place this species within the evolutionary tree of the subfamily, a molecular phylogeny of this group was inferred based on the 12S and 16S mitochondrial genes and the nuclear gene F-reticulon4. The phylogeny indicated that this distinctive species was a member of the subtribe Loricariina. Given its phylogenetic placement, and its unusual morphology, this species is described as a new genus and new species of Loricariinae: Fonchiiloricaria nanodon. This new taxon is diagnosed by usually possessing one to three premaxillary teeth that are greatly reduced; lips with globular papillae on the surface; the distal margin of lower lip bearing short, triangular filaments; the premaxilla greatly reduced; the abdomen completely covered by plates, with the plates between lateral abdominal plates small and rhombic; a caudal fin with 14 rays; the orbital notch absent; five lateral series of plates; dorsal-fin spinelet absent; preanal plate present, large and solid, and of irregular, polygonal shape, the caudal peduncle becoming more compressed posteriorly for the last seven to 10 plates.

A phylogeny of the species of the loricariid genus Acestridium and relevant outgroups is presented based on a parsimony analysis of 52 unweighted and unordered morphological characters. Acestridium is diagnosed as monophyletic based on the possession of the 17 exclusive synapomorphies. Two primary trees were found, and the strict consensus among those alternative trees resulted in the following relationships: ((A. dichromum + A. triplax)(A. gymnogaster + A. scutatum + (A. discus (A. colombiensis + A. martini)))). Acestridium was found to be sister to Niobichthys with this clade subsequently the sister-group to Oxyropsis + Hypoptopoma.Uma filogenia das espécies do gênero de Loricariidae Acestridium e grupos externos relevantes é apresentada com base na análise de parcimônia de 52 caracteres morfológicos não pesados e desordenados. Acestridium é diagnosticado como monofilético com base na posse de 17 sinapomorfias exclusivas. Duas árvores primárias foram encontradas e o consenso estrito entre essas árvores alternativas resultou nas seguintes relações: ((A. dichromum + A. triplax)(A. gymnogaster + A. scutatum + (A. discus (A. colombiensis + A. martini)))). Acestridium foi encontrado como grupo-irmão de Niobichthys e este clado como grupo-irmão sucessivo de Oxyropsis + Hypoptopoma.

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The genus Ixinandria was described in 1979 to include I. steinbachi from the upper río Juramento in northern Argentina and I. montebelloi from the upper río Bermejo in southern Bolivia. We used a multivariate morphometric analysis (Principal Components Analysis) and a molecular comparison of the Cytochrome Oxidase I gene to investigate variation among distinct populations from the known distribution range of both species. We conclude that the populations are not significantly distinct and do not deserve separate species recognition, and we place I. montebelloi in the synonymy of I. steinbachi.O gênero Ixinandria foi descrito em 1979 para incluir I. steinbachi do alto rio Juramento no norte da Argentina e I. montebelloi do alto rio Bermejo no sul da Bolívia. Utilizamos análise morfométrica multivarida (Análise de Componentes Principais) e uma comparação molecular do gene Citocromo Oxidase I para investigar a variação entre populações distintas da área de distribuição de ambas as espécies. Concluímos que as populações não são significativamente distintas e não merecem reconhecimento como espécies separadas, e colocamos Ixinandria montebelloi na sinonímia de I. steinbachi.

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Loricaria luciae, new species, is described from the the rio Paraguay basin of Bolivia, Brazil, and Paraguay, south to its confluence with the rio Paraná in Argentina. It is distinguished from all congeners by the following combination of characteristics: pectoral girdle entirely naked or with small isolated plates near base of pectoral fin, post-ural plate at base of caudal fin large (plate length 17.0-20.3% HL), and total lateral plates 32-33 (modally 32). The new species occurs in a variety of habitats ranging from small, seasonally intermittent streams with clear water to large, turbid rivers over sand and mud substrates. It is sympatric with at least three other species of Loricaria in the Paraguay and lower Paraná drainages, including L. apeltogaster Boulenger 1895, L. coximensis Rodriguez et al. 2012, and L. simillima Regan 1904.