Diagnosis: Hemigrammocharax rubensteini is distinguished from all congeners, except H. lineostriatus, by the presence of a dark, typically continuous, longitudinal band extending from the posterodorsal margin of the opercle to the dark spot overlying the caudal peduncle, vs. a body pigmentation pattern consisting of several vertical bars in H. angolensis, H. machadoi, H. minutus, H. monardi, H. multifasciatus, and H. wittei or lacking a dark longitudinal band in H. ocellicauda and H. uniocellatus (Ref. 93227). Hemigrammocharax rubensteini differs from H. lineostriatus in having the dorsal-fin origin located anterior to the vertical through the pelvic-fin origin, vs. the dorsal-fin origin located posterior to the vertical through the pelvic-fin insertion; 18 to 30 perforated scales along the lateral line, vs. 6 to 9; and 12 to 14 branched dorsal-fin rays, vs. 9 to 11 (Ref. 93227). Hemigrammocharax rubensteini has a variably discontinuous lateral line which in some instances has only a few unpored scales and thus approximates the completely pored lateral line characteristic of the species of Nannocharax; it differs also from the members of that genus with a continuous dark midlateral longitudinal band both in the incompletely pored lateral line, vs. completely pored; and the lower number of total scales along that series, 35-38 vs. 39 or greater in N. ansorgii, N. latifasciatus, N. lineomaculatus, N. parvus and N. usongo (Ref. 93227).

Description: Body slightly elongated and laterally compressed (Ref. 93227). Dorsal profile convex from tip of snout to vertical situated slightly anterior to anterior nares, straight to slightly convex from that point to tip of supraoccipital spine; convex from tip of supraoccipital spine to dorsal-fin origin; straight to slightly convex along dorsal-fin base; straight from insertion of last dorsal-fin ray to posterior terminus of adipose fin base; and straight to slightly concave along caudal peduncle (Ref. 93227). Ventral profile of head convex along anterior portion of dentary; slightly convex from that point to isthmus; ventral profile of body slightly convex from isthmus to pelvic-fin insertion; straight to slightly concave from pelvic-fin insertion to vertical situated anterior to urogenital papillae; concave from that point to anal-fin origin; slightly convex to straight along anal-fin base; and straight to slightly concave along caudal peduncle; ventral surface of body flattened between pelvic-fin insertions (Ref. 93227). Mouth subterminal; premaxilla bearing one tooth row consisting of 6 elongate, bicuspid, slightly distally expanded teeth; dentary bearing one tooth row consisting of 6 elongate, bicuspid, slightly distally expanded teeth; maxilla toothless (Ref. 93227). Unbranched dorsal-fin rays 2-5, branched rays 12-14; tip of pectoral fin falling short of pelvic-fin insertion, unbranched pectoral fin-rays 1, branched rays 8-10; pelvic fin rays i,7,i; unbranched anal-fin rays 1-3, branched rays 7-8 (Ref. 93227). Scales ctenoid; covering all of body; lateral line straight, but incompletely pored with 35-38 scales, pored scales 18-30 (Ref. 93227).

Colouration: Dorsal portion of head olive brown and ventral region white; eye and opercular region brownish with iridescent copper overlay (Ref. 93227). Dorsal and posterior regions of body olive brown; abdominal region white with few melanophores and fainter reticulation pattern than dorsal portion of body; caudal spot round, black, and extending slightly onto bases of middle caudal-fin rays (Ref. 93227). Base of dorsal and ventral caudal-fin lobes white with yellowish tint; dorsal fin slightly yellow; pelvic, anal, and caudal fins hyaline overall other than for scattered melanophores; pectoral fin hyaline (Ref. 93227).