Can be diagnosed from species of the A. facetus, A. forquilha, A. kaaygua and A. scitulus species groups, and from A. acaroides, A. ykeregua, A. angiru and A. taura by having 12 caudal vertebrae (vs. 13 - 15) and 14 precaudal vertebrae (vs. 12 - 13); from species of the A. facetus, A. forquilha and A. kaaygua species groups by having three abdominal bars in all stages of life (vs. always four abdominal bars in juveniles, and adults with three bars in about 50% and four in about 50% of all specimens examined); from A. perdi by having 26 total vertebrae (vs. 25); from A. ykeregua by the absence of dark marks on the suborbital region (vs. presence); from A. agiru by having a conspicuous rounded caudal-fin base spot (vs. spot very narrow or absent); from all its congeners of the A. autrani species group by having anal-fin base squamation beginning at the third anal-fin spine (vs. anal-fin base squamation beginning at the sixth anal-fin spine); from A. autrani, A. barbosae, A. ipatinguensis, A. macaensis, A. macacuensis, A. muriae, A. paraibae, A. robustus, A. saquarema and A. montanus by having fewer proximal radials on anal-fin base (12 in A. mattosi vs. 13 in A. ipatinguensis, A. macacuensis, A. robustus and A. montanus; 13 - 14 in A. autrani, A. barbosae, A. macaensis, A. muriae and A. paraibae; and 14 - 15 in A. saquarema); from A. tavaresi by having mouth isognathous (vs. prognathous); and from A. ribeirae by having last dorsal-fin spine shorter (last dorsal-fin spine length 13.2 - 15.4% SL vs. 16.0 - 16.8% SL) (Ref. 89866).