This species differs from all its congeners except A. verecundus, A. jataiensis, A. reisi, and A. tombador by the absence of an adipose fin; a series of 4 to 6 small median, unpaired platelets forming a low postdorsal ridge covers the area otherwise occupied by the adipose fin. It differs from A. tombador and A. verecundus by the presence of tentacles on the snout of adults (vs. absence or reduction of tentacles), and by a lower number of plates of the dorsal plate series between the end of the postdorsal ridge and the origin of the first plate-like procurrent caudal-fin ray (one or none vs. two or more). It is further distinguished from A. tombador by the predorsal length (45.3-47.1 vs. 42.7-45.1% SL), head depth at supraoccipital (18.7-19.4 vs. 15.6-16.9% SL), cleithral width (32.4-33-6 vs. 27.531.2% SL), body width at dorsal-fin origin (27.8-30.5 vs. 22.826.9% SL), caudal-peduncle length (25.6-27.9 vs. 29.4-32.4% SL), and the number of plates between the anal and caudal fins (9-10 vs. 11-12). It differs from A. reisi and A. jataiensis by a narrower mandibular tooth row (14.8-17.0 vs. 19.4-24.0% HL), fewer teeth (50-59 vs. 62-80 on dentary and 47-55 vs. 61-80 on premaxillary), and by a lower caudal peduncle (8.5-9.4 vs. 9.6-10.7% SL), respectively (Ref. 56914).