Acantopsis ioa is distinguished from all congeners by combination of the following characters: absence of labial barbels; usually lack of distinct small black spot on upper margin of caudal-fin base, 0-1 row of large spots on side of head; absence of large black spots on dorsal or caudal fins; absence of row of black specks beneath midlateral row of black spots; dorsal fin usually with 9½ branched rays and pectoral fin with 10 rays; 15-23 narrow, blotch-like saddles along dorsal midline; 13-21 black spots along side of body, and 46-48 total vertebrae; and body depth 8.5-11.0% SL, body width 5.2-7.9% SL, caudal-peduncle length 13.1-16.2% SL (Ref. 116755).