A new Silver Dollar species of Metynnis Cope, 1878 (Characiformes: Serrasalmidae) from Northwestern Brazil and Southern Venezuela

Abstract

A new Metynnis is described from the rio Negro in Brazil and Venezuela, and from black-or clearwater tributaries in Brazil including the rios Parauari, Uatumã, Trombetas, and Sucunduri (the latter belonging to the rio Madeira basin). The new species can be distinguished readily from all congeners by having a high concentration of dark chromatophores on the lateral line scales. It can be further distinguished by the combination of head length 24.3-27.5% of SL, 13-18 gill-rakers on upper limb and 16-24 gill-rakers on lower limb. The new species is most similar to and likely most closely related to Metynnis hypsauchen. These two species share a similar color pattern, body shape and sexual dimorphism of the anal fin. However, they differ in that M. hypsauchen has a lightly pigmented lateral line. The new species is also distinguished from M. hypsauchen by having 56-65 predorsal scales and 90-104 lateral line scales (vs. 36-54, and 65-82, respectively). A detailed osteological description of the new species is provided.Um novo Metynnis é descrito do rio Negro, no Brasil e Venezuela, e de tributários de água clara ou preta no Brasil, incluindo os rios Parauari, Uatumã, Trombetas e Sucunduri (o último pertencendo à bacia do rio Madeira). A nova espécie pode ser prontamente distinguida de todas as congêneres por possuir escamas da linha lateral com elevada concentração de cromatóforos escuros. Ela pode ser adicionalmente diferenciada por uma combinação de comprimento da cabeça 24,3-27,5% do CP, 13-18 rastros branquiais no ramo superior e 16-24 rastros branquiais no ramo inferior. A nova espécie é mais similar e provavelmente mais proximamente relacionada à Metynnis hypsauchen. Essas duas espécies compartilham padrão de colorido semelhante, forma do corpo e dimorfismo sexual na nadadeira anal. No entanto, elas diferem na presença de linha lateral com pigmentos mais claros em M. hypsauchen. A nova espécie também pode ser distinguida de M. hypsauchen por apresentar 56-65 escamas pré-dorsais e 90-104 escamas na linha lateral (vs. 36-54, e 65-82, respectivamente). Uma descrição osteológica detalhada da nova espécie é fornecida.

One thousand DNA barcodes of piranhas and pacus reveal geographic structure and unrecognised diversity in the Amazon

“…Sharing of species and lineages between the Aripuanã and Guiana Shield rivers is not restricted to the serrasalmids, but has also been observed in cichlids of the genus Symphysodon 70 , 71 and loricariid catfishes 72 . Aside from the three potential lineages of Metynnis luna , there were few new lineages of silver dollars, likely reflecting the recent taxonomic work 22 and ongoing studies being carried out on the group (Ota, studies in progress).…”

“…While the 38 species of piscivorous true piranhas of the genera Serrasalmus , Pygocentrus , Pygopristis and Pristobrycon can be easily diagnosed by their single row of sharp interlocking teeth, the remaining genera–a non-monophyletic group of 56 species commonly known as “pacus” (e.g. Myleus , Myloplus , Piaractus ) or “silver dollars” ( Metynnis )–possess two rows of molariform or incisiform premaxillary teeth 5 , 8 , 19 – 22 . Phylogenetic hypotheses based either on morphological 23 , 24 or molecular 25 , 26 characters have been published.…”

Phylogenomics of piranhas and pacus (Serrasalmidae) uncovers how convergent diets obfuscate traditional morphological taxonomy

“…The taxonomy and systematics of Serrasalmidae have a long-checkered past “fraught with confusion and instability” (Nico et al, 2018:172). Recent morphological studies have helped distinguish and diagnose a variety of valid genera and species (e.g., Pereira and Castro, 2014; Andrade et al, 2016a; 2016b; 2016c; 2017; 2018; 2019b; Ota et al, 2016; Mateussi et al, 2018; Nico et al, 2018; Escobar et al, 2019). The current study provides robust molecular support for recognizing three major lineages of Serrasalmidae at the subfamilial rank: Colossominae (pacus common to lowland, white water habitats), Myleinae (pacus common to upland clear- and black water habitats), and Serrasalminae (Metynnis and piranhas, cosmopolitan).…”

New remarkable sexually dimorphic miniature species of Hyphessobrycon (Characiformes: Characidae) from the upper Rio Tapajós basin

“…According to Rapp Py‐Daniel & Fernandes (), fishes are particularly interesting and informative organisms in studies of sexual dimorphism due to many specializations found between the sexes. Characiformes is one of the largest components of the freshwater fish fauna world‐wide, spanning numerous examples of sexual dimorphism (Weitzman & Cobb, ; Vari, ; Weitzman & Palmer, ; Zanata & Vari, ; Menezes & Weitzman, ; Gama, ; Malabarba & Jerep, ; Zanata & Camelier, ; Ota et al, ). Such cases are particularly profuse in Characidae, the most diverse family of the order (Mirande, ; Oliveira et al, ).…”