The morphological ontogeny of Achipteria gigantea sp. nov. from northern Spain is described and illustrated. The adult of this species is the largest of known species of Achipteria Berlese, 1885, and has seta in inserted on the inner part of wide lamella, approximately 1/3 of the total length from its base, which is rare in this genus; most species have this seta inserted near the base of the lamella. The tarsi of A. gigantea are heterodactylous and dorsally serrate, but the outer claws are thinner and has longer dens than the middle claw. The juveniles of A. gigantea are plicate, as other species of Achipteria, but the subsequent instars are larger than congeners and most gastronotal setae are thicker and with denser barbs than in other species; some setae on femora, genua and tibiae on legs are also thicker. The leg claws of juveniles of A. gigantea are also serrate, but in the larva the dens are longer than in the nymphs. The ontogeny of A. gigantea is compared with that of congeners, and the morphology of the adult of this species is compared with other species of Achipteria. Three subgenera of Achipteria (Cubachipteria Balogh & Mahunka, 1979, Izuachipteria Balogh & Mahunka, 1979 and Hokkachipteria Balogh & Mahunka, 1979) and Parachipteria Hammen, 1952 are provisionally considered as junior synonyms of Achipteria.