The morphological ontogeny of Melanozetes stagnatilis (Hull, 1914) is described and illustrated. The juveniles of this species have a humeral organ and a humeral macrosclerite, bearing seta c₁, which occur in most species of Sphaerozetinae (Ceratozetidae), but also have well-developed lamellae, without the translamella, which is unique in Sphaerozetinae. The juveniles have a gastronotal shield, with seven pairs of setae in the larva (d-, l-series and h₁), and 10 pairs in the nymphs (d-, ₁-, h-series and p₁), and setae p₂ and p₃ are inserted on a large ventral macrosclerite. The legs of juveniles and adult are stocky, with large and flattened femora I and II, having a large ventral carina. The adult of M. stagnatilis has well-developed lamellae, with a translamella, and 14 pairs of notogastral setae, but the number of porose areas varies from six to eight, which is unique in MelanozetesHull, 1916.