Distinguished from all other congeneric species except Harttiella pilosa by the frequent presence of few small preanal plates (vs absence of preanal plates), and by its specific barcode sequences (JF292277, JF292278, JF292279, JF292280, JF292282, JF292283). Differs from Harttiella pilosa by having the pectoral girdle wider than pelvic girdle (vs pectoral girdle approximately as wide as the pelvic girdle). Six unique morphometric variables distinguish Harttiella longicauda from all other congeners: shorter pelvic

spines (mean = 19.36 ± 1.17% of SL vs 20.55 ± 0.36 < mean < 24.67 ± 1.46% of SL); smaller

body width at eighth postdorsal plate (mean = 9.29 ± 1.07% of SL vs 10.28 ± .98 < mean < 11.48 ± 0.94% of SL); body width at fourteenth postdorsal plate (mean = 3.99 ± 0.51% of SL vs 4.72 ± 0.62 < mean < 5. 59 ± 0.70% of SL); minimum caudal peduncle depth (mean = 2.53 ± 0.18% of SL vs 3.24 ± 0.2 1 < mean < 4.86 ± 0.43% of SL); interorbital width (mean = 33.82 ± 2.03% of HL vs 35.25 ± 1.21 < mean < 38.20 ± 2.03% of HL), and head depth at internostril (mean = 33.19 ± 1.76% of HL vs 33.89 ± 2.22 < mean < 36.74 ± 4.00% of HL (Ref. 90209).