Distinguished from all other species of Harttia except Harttia fluminensis and Harttia trombetensis by having an incomplete abdominal cover restricted to preanal and abdominal lateral plates with a row of platelets joining these two series of plates (vs. absence of row of platelets making junction between preanal and lateral abdominal plates), and by its specific barcode sequence (JF292262). Differs from Harttia fluminensis by having a shallower head (31.96-38.77, mean 36.52 ± 1.80% of HL, vs. 37.31-43.30, mean 38.94 ± 1.42% of HL); and from Harttia trombetensis by the color pattern of the caudal fin (a dark rounded blotch at base of caudal fin, vs. a large dark band). Four morphometric

variables strictly characterize Harttia tuna: longer head (mean = 24.97 ± 1.14%

of SL vs 23.19 ± 1.33 < mean < 24.15 ± 1.38% of SL); greater predorsal length (mean = 33.58 ± 0.84% of SL vs. 32.10 ± 1.05 < mean < 33. 01 ± 1.11% of SL); smaller postdorsal length (mean = 55.44 ± 1.10% of SL vs 56.63 ± 0.94 < mean < 57.35 ± 1.26% of SL); and smaller orbital diameter (mean = 20.97 ± 1.12% of HL vs. 22.68 ± 1.43 < mean < 23.37 ± 1.08% of HL) (Ref. 90209).