Gymnotocinclus anosteos is a species of armored catfish endemic to Brazil, where it is found in the Tocantinzinho River in the Tocantins River basin. It is the only species in the genus Gymnotocinclus. This species is unusual among the Loricariidae due to its extremely reduced armor plates that are characteristic of the family, giving the fish a relatively naked body. This fish probably has a basal position in the subfamily Hypoptopomatinae. This species grows to a length of 4.4 centimetres (1.7 in) SL.