4.7 cm SL (male/unsexed; (Ref. 82468))
Jupiaba iasy is distinguished from J. acanthogaster, J. atypindi, J. keithi, J. maroniensis, J. meunieri, J. minor, J. pinnata, and J. poekotero by having teeth with the central cusp distinctly larger than the lateral cusps and dentary teeth abruptly decreasing in size posteriorly (vs. teeth cusps similar in size and dentary teeth gradually decreasing in size posteriorly). The new species differs from J. abramoides, J. anteroides, J. apenima, J. asymmetrica, J. pirana, J. polylepis, J. poranga, J. potaroensis, J. yarina, and J. zonata by having 3435 lateral line scales (vs. 3966). It can be further distinguished from J. polylepis, by having 1921 branched anal-fin rays, horizontal eye diameter 42.145.8% and clearer overall body scales (vs. 2428 branched anal-fin rays, eye diameter 28.641.8%, and overall body darker). Jupiaba iasy can also be distinguished from J. elassonaktis, J. essequibensis, J. mucronata, and J. scologaster (as well as all the aforementioned species) by its color pattern that consists of a single posteriorly displaced dark moon-shaped and vertically elongated humeral blotch, encompassing the first 5 to 7 lateral line scales, extending vertically through four longitudinal scales series above lateral line and two series below it (vs. longitudinally elongatedhumeral blotch in J. mucronata, and two humeral blotches in J. essequibensis, J. elassonaktis, and J. scologaster), and an inconspicuous dark spot over the proximal portion of the medial caudal fin rays (vs. caudal spot inconspicuous in J. essequibensis, and J. elassonaktis and completely absent in J. mucronata and J. scologaster). Jupiaba iasy is distinguished from J. ocellata by having 1921 branched anal-fin rays (vs. 2327), 810 predorsal scales arranged in a regular row (vs. 1012, irregularly arranged), six longitudinal series of scales above lateral line (vs. 88,5), and four series below it (vs. 67), lower body depth (32.336.1%,X=34.1% SL vs. 36.450.0%, X=41.2% SL), and lack of filamentous first dorsal and anal-fin rays (vs. filamentous rays present) (Ref. 82468).