Trichomycterus guaraquessaba is a species of pencil catfish presently only known from Rio Bracinho, a small isolated river in Paraná state, Brazil. This is an elongate catfish up to 91.5 centimetres (36.0 in) standard length. It has no unique morphological features and can be distinguished from its congeners by a combination of characters including a uniformly grey colouring with only small dark spots on the flank, pelvic fin not covering the urogenital opening and square-ended caudal fin.