The morphology of species of Platynothrus Berlese, 1913 is insufficiently known. For example, in most species the number of hyposthomal setae, which is probably species-specific, is unknown. Moreover, the number of leg setae and their chaetotaxy are poorly documented which might cause difficulties in identification and species comparison. In this paper, the morphological ontogeny of Platynothrus punctatus (L. Koch, 1879) is redescribed and illustrated and this species is further characterised using DNA barcoding techniques. In all juveniles the bothridial seta is minute, exobothridial seta exa is short and exp is alveolar. In the larva, seta f₁ is setiform, but in the nymphs it is alveolar. Most prodorsal and gastronotal setae of the larva are short and of nymphs are of medium size. The larva has one pair of hyposthomal setae m, protonymph has two pairs, whereas the deutonymph, tritonymph and adult have three, four and five pairs respectively. During the ontogeny of this species, additional l seta appear on trochanter III and all femora, and l and v setae on tarsi. The number of setae on femora of deutonymph to adult is considered species-specific. In all instars, seta d coupled to solenidion is present on all genua and tibiae.