The morphological ontogeny of Platyliodes scaliger (C.L. Koch, 1839) is described and illustrated. The adult of this species has a flattened notogaster, with two pairs of leaf-like setae on its posterior end. The adult and nymphs carry the exuvial scalps of previous instars on the dorsal part of the hysterosoma. The cuticle of the juveniles is plicate, and the larva has 10 pairs of gastronotal setae (c₁ and dp absent), whereas the nymphs have six pairs (h- and p-series). The nymphs also have a posterior excrescence, which bears a long, setiform seta h₁, and a clearly shorter, leaf-like seta p₁. During the ontogeny of P. scaliger, the number of gastronotal setae is highly reduced from 10 pairs in the larva to six pairs in the nymphs, and four pairs in the adult (h₁ and p-series remain).