Abstract
ABSTRACT A new species of the characid genus Knodus is described from the rio Aripuanã (rio Madeira basin). It can be distinguished from its congeners by its very low body depth, the presence of tri- to pentacuspid teeth on the outer premaxillary series, with the median cuspid larger than the lateral ones, the teeth of the inner premaxillary series pentacuspid, distinctly larger than those of the outer series, the maxillary teeth tri- to pentacuspid, with the median cusp slightly larger than the lateral ones, the four anteriormost dentary teeth pentacuspid, the smaller posterior teeth tri- to pentacuspid, a complete lateral line with 36-38 scales, 3 longitudinal scale series from pelvic fin origin to lateral line, and 11-12 circumpeduncular scales. The new species is also compared to incertae sedis species of ‘Bryconamericus’ from northern South America since phylogenetic studies suggest a closer relationship of those species with Knodus.
Highlights
The speciose genus Knodus Eigenmann, 1911 currently includes 28 valid species (Fricke et al, 2020) of small-sized fishes (30 to 90 mm SL; van der Sleen et al, 2018), mainly occurring in the Amazon basin, but with representatives distributed in all main drainages of cis-Andean South America (Lima et al, 2004; Ferreira, Netto-Ferreira, 2010; Esguícero, Castro, 2014)
Besides being plesiomorphic characters within the Stevardiinae or the Characidae (Malabarba, Weitzman, 2003; Weitzman et al, 2005; Mirande, 2010), a considerable plasticity has been documented within both genera for each of the diagnostic characters, and the sole character allowing the distinction from each other is based on the presence of scales covering half the extent of caudal-fin rays in Knodus, or being restricted to the base of that fin in Bryconamericus (Eigenmann, 1911; Schultz, 1944; Ferreira, Netto-Ferreira, 2010; Esguícero, Castro, 2014; Dagosta, NettoFerreira 2015)
Given the controversy involving the extent of caudal fin squamation distinguishing Bryconamericus and Knodus, some authors have rejected its validity as a diagnostic character between these genera, or even proposing the synonymy of Knodus with Bryconamericus
Summary
The speciose genus Knodus Eigenmann, 1911 currently includes 28 valid species (Fricke et al, 2020) of small-sized fishes (30 to 90 mm SL; van der Sleen et al, 2018), mainly occurring in the Amazon basin, but with representatives distributed in all main drainages of cis-Andean South America (Lima et al, 2004; Ferreira, Netto-Ferreira, 2010; Esguícero, Castro, 2014). 2008), K. deuterodonoides (Eigenmann, 1908), among others), the current composition of Knodus, as suggested by Thomaz et al (2015), comprises Bryconadenos Weitzman, Menezes, Evers, Burns, 2005, Rhinopetitia Géry, 1964 (see comments in Netto-Ferreira et al, 2016, Netto-Ferreira, Vari, 2017; Menezes, NettoFerreira, 2019), and likely Phallobrycon Menezes, Ferreira, Netto-Ferreira, 2009 Despite such taxonomic adjustments in the composition of those genera, no morphological diagnoses were provided, not allowing accurate generic allocation of the species not included in both studies or new to science. The new species is compared to representatives of Bryconamericus from northern South America, since the composition of both genera is likely to be further modified in future studies, considering the possible closer relationship between ‘Bryconamericus’ from northern South America with Knodus, suggested by the aforementioned studies (Thomaz et al, 2015; Mirande, 2019)
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