This species can be distinguished from Potamorrhaphis eigenmanni and P. guianensis by having the posterior third of the labial membrane highly expanded laterally, reaching to or passing the level of the ventral margin of the maxilla when folded ventrally (vs. narrow, not reaching the level of the ventral margin of the maxilla when folded ventrally); from P. eigenmanni by having 3 rows of accessory teeth on the lower jaw (vs. 2 rows), and 115-128 scales on the lateral line (vs. 97-119); from P. guianensis by having the contralateral branchiostegal membranes overlapping in the midventral line (vs. branchiostegal membranes not overlapping ventrally), 3 rows of accessory teeth on the lower jaw (vs. 4 rows), and dentary with coronoid process salient (vs. coronoid process not salient); from P. petersi by the coloration of the labial membrane with melanophores only in the inner margin (vs. melanophores uniformly distributed), 29-34 dorsal-fin rays (vs. 35-43), 25-29 anal-fin rays (vs. 30-39), deeper caudal peduncle (2.1-2.7 vs. 1.1-1.6% BL), longer predorsal length (62.9-67.6 vs. 59.5-62.8% BL), longer pectoral-pelvic distance (38.5-42.6 vs. 36.0-38.1% BL), and longer head length (17.6-18.9 versus 15.8-17.9% BL) (Ref. 92518).