Knodus figueiredoi differs from all other species of the genus by having only tricuspid teeth in the inner premaxillary row (vs. teeth with 5 or 7 cusps). It can be further distinguished from all its congeners by having i,5,i (vs. i,6,i or i,7) pelvic-fin rays. It can be diagnosed from K. breviceps and K. savannensis in having a conspicuous, round humeral blotch (vs. inconspicuous, vertically elongate). It can be further distinguished from K breviceps in having five (vs. six) longitudinal scale rows between the dorsal-fin origin and lateral line, and from K. savannensis in having branched anal-fin rays 15-17 (vs. 20-21), and a hyaline caudal fin (vs. dark longitudinal band on lower caudal-fin lobe). It can be differentiated from Bryconamericus novae, the only species of the genus in the Araguaia-Tocantins basin, in having a conspicuous, round (vs. inconspicuous, vertically elongate) humeral blotch, 15-17 branched anal-fin rays (vs.18-20); five (vs. four) longitudinal scale rows between the dorsal-fin origin and lateral line; four large tricuspid teeth in the dentary (vs. pentacuspid); and presence of scale rows covering the basal portions of the caudal-fin lobe (vs. absence) (Ref. 97362).