Tuesday, July 5, 2016

[Ichthyology • 2016] Moenkhausia mutum • A New Species of Moenkhausia Eigenmann (Characiformes: Characidae) from the rio Arinos Basin, Brazil


Moenkhausia mutum 
 Dagosta & Marinho, 2016

ABSTRACT

A new species of Moenkhausia is described from the rio Arinos drainage, rio Tapajós basin, Mato Grosso, Brazil. The new species is diagnosed from all congeners, except M. hemigrammoides, M. nigromarginata , and Moenkhausia rubra by having intense diffuse dark pigmentation on the dorsal and anal fin-rays. The new species can be distinguished from the above mentioned species by the combination of 20-23 branched anal-fin rays, presence of a vertically elongate roughly rectangular humeral spot surpassing the lateral line ventrally, absence of a well-defined black spot on the distal portion of the dorsal fin and lack of a series of longitudinal dark zigzag stripes on body. The new species is herein described along with a report and discussion of a possible connection between the rio Tapajós and rio Paraguay basins, near Diamantino Municipality, Mato Grosso.

Key words: Headwaters; Juruena; Moenkhausia nigromarginata; Moenkhausia rubra; Tapajós

Fig. 1. Moenkhausia mutum, new species, Brazil, Mato Grosso, Nova Mutum, rio Arinos drainage, rio Tapajós basin: 
(a) holotype alcohol preserved, MZUSP 117071, 65.3 mm SL, (b) paratype, live coloration, MZUSP 117072, 53.6 mm SL, collected with the holotype, (c) holotype, live coloration.  
Diagnosis. Moenkhausia mutum is distinguished from all congeners, except M. hemigrammoides , M. nigromarginata and Moenkhausia rubra by having intense diffuse dark pigmentation on the dorsal and anal fin-rays, especially in anteriormost rays and in the distal portion (vs . fins hyaliane or only with scattered chromatophores). It can be distinguished from M . rubra by the number of branched anal-fin rays 20-23, modally 21 (vs . 17-20, modally 19) and by having a vertically elongate humeral spot (vs. approximately rounded), from M. hemigrammoides by having pelvic fin intensely dark pigmentated (vs . hyaline), by the anal fin with a relative diffuse dark pigmentation (vs . presence of a black oblique line extending from the urogenital cavity to the tip of second or third branched anal-fin ray), and by lacking a well-defined black spot on the distal portion of the dorsal fin (vs. present), and from M. nigromarginata by lacking a series of longitudinal dark zigzag stripes on body formed by the concentration of dark chromatophores in the upper and lower portions of the exposed area of scales (vs. presence) and by having a vertically elongate roughly rectangular humeral spot surpassing the lateral line ventrally (vs. humeral spot approximately rounded, with an anteroventral projection not surpassing the lateral line ventrally).

Etymology. The specific name mutum is in allusion to the Brazilian popular name of the curassow birds of the genus Crax Linnaeus, which are typically dark colored, as well as the fins of Moenkhausia mutum. Also, the name refers to the Nova Mutum Municipality, the type locality, and where most of the type specimens were collected. A name in apposition.

Geographic distribution. Moenkhausia mutum is known from the rio Arinos drainage, tributary of rio Juruena, upper rio Tapajós basin, Mato Grosso State, Brazil.


Fernando C. P. Dagosta and Manoela M. F. Marinho. 2016. A New Species of Moenkhausia Eigenmann (Characiformes: Characidae) from the rio Arinos Basin, Brazil. Neotrop. ichthyol. 14(2);   DOI: 10.1590/1982-0224-20150052

RESUMO: Uma espécie nova de Moenkhausia é descrita das drenagens do rio Arinos, bacia do rio Tapajós, Mato Grosso, Brasil. A nova espécie é diagnosticada de todas as congêneres, exceto M . hemigrammoides , M . nigromarginata , e Moenkhausia rubra por possuir pigmentação escura intensa e difusa nos raios das nadadeiras dorsal e anal. A nova espécie pode ser distinguida das espécies supracitadas pela combinação da presença de 20-23 raios ramificados na nadadeira anal, presença de uma mancha umeral aproximadamente retangular, ultrapassando a linha lateral ventralmente, ausência de uma mancha negra conspícua na porção distal da nadadeira dorsal e pela ausência de uma série de linhas longitudinais negras em forma de zigue-zague no corpo. A nova espécie é aqui descrita, juntamente com o relato de uma possível conexão entre as bacias dos rios Tapajós e rio Paraguay, próximo ao município de Diamantino, Mato Grosso.




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