Sesommata platysaris is a moth of the Palaephatidae family. It was described by Meyrick in 1931. It is found in the lake region in Argentina, including Lago Lacar and especially Lago Nahuel Huapi. The length of the forewings is 4.8-6.2 mm for males and 5.4-5.6 mm for females. Adult males have dark fuscous to black wings, with arelatively large, rounded mass of broad sex scales. The forewings of the females are smooth and sometimes have a few scattered whitescales. Adults are on wing from November to January in one generation per year.