Xenurobrycon polyancistrus is a species of characid fish of the subfamily Glandulocaudinae.

A freshwater fish, it is the smallest species of characin in its family and order.

[1] Found in the gallery forest pools adjacent to rivers in savannah areas of the Rio Mamore and Rio Isiboro drainages in Bolivia.

[2] It is also found in the Río Madre de Dios basin in Peru.

It was found among a collection of fishes from Bolivia sent by Gerard Loubens of the Office de la Recherche Scientifique et Technique Outre-Mer, Laboratoire d'Ichthyologie de l'Universite de Trinidad, Estado Beni, Bolivia.