The morphological ontogeny of Achipteria magna (Sellnick, 1928) is described and illustrated. The adult of this species has many morphological characters of Achipteria Berlese, 1885, such as long and wide lamellae, fused in the medial part, long anterior pteromorphic projections, and 10 pairs of notogastral setae, with longer c₂ and la. However, this species has many fine pores on the notogaster and a pair of saccules S1, instead of four pairs of saccules or porose areas that occur in most species of Achipteria. In A. magna, anteroventral apophysis on genua I and II is present, genu IV is longer than tibia IV, seta bv″ on femur II is longer than seta d, seta v″ on this segment is more than twice longer than seta bv″, seta l′ on femur III is short and leg claws are smooth. The juveniles of this species are stocky, with the prodorsal setae minute or short and smooth. The gastronotal setae of the larva are short or of medium size, thick and barbed, except for minute c₂, c₃ and h₃. In the nymphs, all setae are thick and barbed, but c₂ and c₃ are shorter than c₁, and p₂ and p₃ are shorter than p₁. The morphological ontogeny of A. magna is compared with some congeners, and Pseudachipteria Travé, 1960 and Campachipteria Aoki, 1995 are considered junior synonyms of Achipteria. The ecology and some biological parameters of A. magna are also investigated.