Range extension of the miniature pencil-catfish Potamoglanis wapixana (Siluriformes: Trichomycteridae) into the Essequibo River basin, Guyana.

Morphological examination of Potamoglanis specimens from three localities in the Essequibo River basin, Guyana, and one location in the Branco River basin, Brazil, confirmed their identification as Potamoglanis wapixana - a species originally described from only the Branco River basin. Morphological similarity of these miniature catfishes on opposite sides of the Rupununi savannah watershed divide and new records from lentic habitat suggest that either their modern populations predate the Pliocene division of the Branco and Essequibo rivers or the species is capable of living in and/or migrating across the Rupununi Portal - a seasonally flooded hydrological connection known to facilitate the movement of mostly much larger fishes between the Branco and Essequibo basins.