A new shallow-bodied species of Moenkhausia is described from the upper Rio Negro, Amazon basin, Brazil. The new species is diagnosed from all congeners by the combination of a body depth not surpassing 33% in SL in adult specimens, seven scale rows between dorsal-fin origin and lateral line, five scale rows between pelvic-fin insertion and lateral line, a single conspicuous vertically elongated humeral blotch, and a conspicuous caudal peduncle blotch extending to the distal margin of the median caudal-fin rays. The new species was collected together with Jupiaba zonata, with which it shares a very similar color pattern. The similarity between these two taxa is interpreted as an additional case of Batesian mimicry between Moenkhausia and Jupiaba.
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