The São Domingos karst in the upper Tocantins basin is home to an unusually high number of cavefish species (more than any other region in the Americas): Ancistrus cryptophthalmus, several Ituglanis species, Pimelodella spelaea, Aspidoras mephisto, an undescribed Cetopsorhamdia species and Eigenmannia vicentespelaea.Romero, Aldemaro, editor (2001). The Biology of Hypogean Fishes. Developments in Environmental Biology of Fishes. Caserta Tencatt; L. F.; and M. Elina Bichuette (2017). Aspidoras mephisto, new species: The first troglobitic Callichthyidae (Teleostei: Siluriformes) from South America. PLoS ONE 12(3): e0171309. The last is the only known cave-adapted knifefish and one of only two known non-catfish in caves of the South American mainland (the other is the characid Stygichthys typhlops).
