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A new miniature species of the freshwater fish genus Priocharax is described from the Rio Jamari, Rio Madeira drainage, Amazon basin. Priocharax varii sp. n. is the fourth species currently recognized in the genus and shares with the other three the presence of a conspicuous larval pectoral fin in adults, a fully toothed maxilla, a triangular pseudotympanum situated anterior to the fifth vertebra and a tiny size combined with a translucent body. The new species is diagnosed from congeners in having an adipose fin, a unique feature within Priocharax. Molecular identification of the new species and the other valid Priocharax species supports the morphological findings. A brief discussion on the presence/absence of the adipose fin in Characiformes is provided.
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Mattox et al. (2020) studied this question.