Friday, September 15, 2017

[Ichthyology • 2017] Hyphessobrycon myrmex • A New Sexually Dichromatic Miniature Hyphessobrycon (Characiformes: Characidae) from the Rio Formiga, upper Rio Juruena basin, Mato Grosso, Brazil, with A Review of Sexual Dichromatism in Characiformes


Hyphessobrycon myrmex 
Pastana, Dagosta & Esguícero, 2017

Abstract

Hyphessobrycon myrmex sp. nov., is described from the Rio Formiga, upper Rio Juruena, upper Rio Tapajós basin, Mato Grosso, Brazil. The new species can be distinguished from congeners by having the lower half of the body deeply pigmented with dark chromatophores, chromatophores concentrated above the anal fin and forming a broad, diffuse, dark midlateral stripe and by having a dense concentration of dark chromatophores along unbranched dorsal-fin rays and distal portions of the two or three subsequent branched rays. In life, H. myrmex exhibits a conspicuous sexual dichromatism, with adult males red to orange and females and immatures pale yellow. A list containing 108 sexually dichromatic taxa in six families of Characiformes is provided and the distribution of this poorly known type of dimorphism across the Characiformes is discussed.

Key words: Amazon basin; miniaturization; Neotropical ichthyofauna; sexual dimorphism; Tapajós.


Hyphessobrycon myrmex
 (a) Male, 21·6 mm standard length (LS) and (b) female, 19·5 mm LS, MZUSP 118672, paratypes. 
  
Hyphessobrycon myrmex

Etymology: The specific epithet myrmex is derived from the Greek word for ant, in allusion to the small size of adult specimens of the species and also refers to the type locality, the Rio Formiga, which means ‘Ant River’ in Portuguese.




M. N. L. Pastana, F. C. P. Dagosta and A. L. H. Esguícero. 2017. A New Sexually Dichromatic Miniature Hyphessobrycon (Teleostei: Characiformes: Characidae) from the Rio Formiga, upper Rio Juruena basin, Mato Grosso, Brazil, with A Review of Sexual Dichromatism in Characiformes. Journal of Fish Biology.  DOI: 10.1111/jfb.13449

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