Brazilian scientists have described a new species of the tetra genus Moenkhausia from the Rio Tocantins drainage in Brazil (part of the Amazon River drainage).
Publishing their results in a recent issue of the journal Zootaxa, Paulo Lucinda, Luiz Malabarba and Ricardo Benine have described Moenkhausia hysterosticta, the name coming from the Greek hysteros, meaning posterior and stictus spot, in reference to the posteriorly-located humeral spot in this species.
Moenkhausia hysterostricta can be distinguished from other members of the genus in having a dark spot on the upper caudal-fin lobe and a large, irregular dark humeral spot located above the fifth to ninth perforated scale of the lateral line.
Besides the population in the Rio Tocantins, the authors also found a population in the Rio Apure drainage (part of the Orinoco River drainage) in Venezuela which they tentatively consider to also belong to M. hysterosticta.
The Rio Apure population differs from the Rio Tocantins population in having different anal-fin ray (26"29, mean 27.5 vs. 24"27, mean 25.6) and dentary tooth (13"17, mean 14.0 vs. 9"15, mean 12.7) counts, but otherwise shows strong overlap in other morphometric and meristic characters.
The new species is described as a species of Moenkhausia, but the authors acknowledge that the monophyly of the genus has yet to be established.
The new species is placed in Moenkhausia because ...it better conforms to the current definition of the genus... which is defined as the presence of premaxillary teeth in two parallel rows, five or more teeth in the inner premaxillary tooth row, a completely pored lateral line and scaled caudal-fin lobes.
For more information, see the paper: Lucinda, PHF, LR Malabarba and RC Benine (2007) On a new species of the genus Moenkhausia Eigenmann (Ostariophysi: Characidae). Zootaxa 1525, 61"68.