The lack of a dark humeral mark distinguishes Attonitus ephimeros from Attonitus irisae which has a distinct, vertically-elongate humeral bar. The presence on the body wall above the anal-fin base of a band of dark pigmentation which is distinctly wider over the second and third branched anal-fin rays and has a rounded anterior margin in Attonitus ephimeros separates that species from Attonitus bounites which lacks such pigmentation.

Description: Dorsal-fin with 2 unbranched and 8 branched rays. Anal-fin with 3 unbranched and 14-17, typically 15-16, branched rays (Ref 53400).