Distinguished from all other species of Hemigrammus, except Hemigrammus levis, by lacking a humeral spot and the presence of a conspicuous black spot, restricted to caudal fin, roughly triangular or rectangular, extending from base to tip of middle caudal-fin rays (its greatest depth at base of caudal-fin rays). Can be differentiated from Hemigrammus levis by the following characters: anal fin with 18-23 (mode 21) unbranched rays (vs. 16-18); largest tooth of the inner row of premaxilla and dentary with 5 cusps (vs. 7-9); anterior portion of longitudinal band as a broad uninterrupted pigmented area (vs. anterior portion of longitudinal band with a small round concentration of chromatophores at humeral region, surrounded by unpigmented areas anterior and posteriorly); distance of snout to anal-fin origin 58.6-65.9% SL, mean 62.0% (vs. 63.7-73.9% SL, mean 68.8%); anal base length 25.1-32.5% SL, mean 29.2% (19.3-24.7% SL, mean 22.0%), upper jaw length 39.6-48.3% HL (vs. 34.3-39.5% HL) (Ref. 74938).

Description: Longitudinal scale series including pored scales 26-34. Dorsal fin ii9; Anal fin iii,18, 19, 20, 21, 22 or 23; Pectoral fin i9, 10, 11 or 12; Pelvic fin i6 or 7 (Ref. 74938).