Abstract
Abstract A new species of Moenkhausia is described from the rio Machado drainage, Amazon basin, Brazil. It is diagnosed from congeners by its color pattern, consisting of the concentration of chromatophores on the anterior portion of body scales, the horizontally elongate blotch on caudal peduncle, a bright golden coloration of the dorsal portion of eye when alive, and a dark line crossing the eye horizontally. The new species has variable morphology regarding trunk lateral-line canals. Most fully grown individuals do not have enclosed bony tube in many lateral line scales, resembling early developmental stages of tube formation of other species. This paedomorphic condition is interpreted as a result of developmental truncation. Such evolutionary process may have been responsible for the presence of distinct levels of trunk lateral line reductions in small characids. Variation in this feature is common, even between the sides of the same individual. We reassert that the degree of trunk lateral-line tube development must be used with care in taxonomic and phylogenetic studies, because reductions in the laterosensory system may constitute parallel loss in the Characidae. We suggest the new species to be categorized Near Threatened due to the restricted geographical distribution and continuing decline in habitat quality.
Highlights
Moenkhausia Eigenmann, 1903 is the third most species-rich genus among Amazonian fishes, behind only of Corydoras Lacepède, 1803 and Hyphessobrycon Durbin, 1908 (Dagosta, de Pinna, 2019)
This paper aims to describe the new species in detail and to discuss trunk lateral-line morphology in the Characidae, considering the evolutionary development of this character and the systematic of the family
Standard length (SL) and notochord length (NL) is expressed in millimeters and all other measurements are expressed as percentage of SL, except for subunits of head, which are expressed as percentage of head length (HL)
Summary
Moenkhausia Eigenmann, 1903 is the third most species-rich genus among Amazonian fishes, behind only of Corydoras Lacepède, 1803 and Hyphessobrycon Durbin, 1908 (Dagosta, de Pinna, 2019). The genus was defined in a precladistic view, considering a combination of characters of common occurrence in the Characidae, which are premaxillary teeth in two rows, with at least five teeth in the inner row, caudal fin partially covered by scales, and all scales of the lateral line trunk canal pored (Eigenmann, 1917) This classification criterion of Eigenmann (1917, 1918, 1921), efficient for decades, has been subject to criticism since most of the characters used to diagnose genera are known to have independently evolved within the family (Mirande, 2010, 2018).
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