Austrolebias araucarianus can be diagnosed from all congeners by the difference of the color pattern of males and females. The unpaired fins in males consist of yellowish grey bars parallel to fins rays on basal and middle portion, sometimes with transverse connections. Females have dark spots on trunk which are vertically elongated, often forming short bars. It can be further separated from other species of Austrolebias by having rudimentary or the absence of pelvic and pelvic-fin girdle (vs. well-developed, except in two specimens of A. carvalhoi lacking pelvic fin) and the first three neuromasts of the supraorbital series separated from the remaining neuromasts by an interspace (vs. continuous). It is similar to other species of the subgenus Acrolebias (A. carvalhoi and A. varzeae) and differs from species of the subgenera Cypholebias and Megalebias by having 9 gill rakers on the ventral portion of the first branchial arch (vs. 11-16); 17-22 neuromasts around the orbit (vs. 23-38); 2-3 neuromasts on the otic series (vs. 4-10), and preopercular and mandibular series of neuromasts separated (vs. united), and from species of Cypholebias by having shorter pectoral-fin in males extending to the urogenital papilla (vs. reaching between bases of 2nd and 6th anal-fin rays). It also differs from A. carvalhoi and A. varzeae by having 31-33 scales in the longitudinal series (vs. 27-29 in A. carvalhoi and 28-30 in A. varzeae) and 12-14 neuromasts in the supraorbital series (vs. 17-18). It can be separated also from A. varzeae and all species of the subgenera Cypholebias and Megalebias by having 23-25 caudal-fin rays (vs. 28-29 in A. varzeae, 26-32 in species of Cypholebias and 29-36 in Megalebias) and frontal squamation G-pattern (vs. F-patterned in A. varzeae and species of Cypholebias, and irregularly arranged in Megalebias) (Ref. 97355).

Description: Pelvic-fin rays 1-5 or absent; caudal fin rounded (Ref. 97355).