Distinguished from all congeners by the following combination of characters: hypermorphosis of sphenoid region of the neurocranium in both males and females; ossified lateral ethmoid; uniformly brown body coloration other than for white or yellow band on the chin, dorsal surface of head, and mid-dorsal part of body; presence of a white or yellow band on chin, dorsal surface of head, and mid-dorsal part of body; unpigmented band encircling base of caudal fin. Males differ from the holotype of Apteronotus macrostomus, which is presumably a male, by the following characters: head length 18.6-20.3% of length to end to anal fin [LEA] vs. (21.4); head width 25.3-36.5% of HL (vs. 39.3); head depth at eye 37.9-39.4% of HL (vs. 50.1); snout length 40.0-43.8 % HL (vs. 44.7); and distance from posterior naris to eye 17.8-20.3% of HL (vs. 23.6); width of mouth 40.6-50.1% (vs. 56.2); interocular width 14.1-18.6% HL (vs. 19.9); and postocular distance 49.2-58% HL (vs. 62.1). In addition, males can be separated from the holotype of Apteronotus leptorhynchus, presumably also a male, by the following features: length of anal-fin base 70-79% of LEA (vs. 83.7); head length 18.6-20.3% of LEA (vs. 21); head width 25.3-36.5% of HL (vs. 37.3); and head depth at eye 37.9-39.4 % of HL (43.6) (Ref. 75033).