Аннотация:Miniaturization is a major evolutionary trend prominent in insects. Diminution of body size in some insect groups has resulted in insects comparable in size to some unicellular protists. The nervous systems and sense organs of insects have been considerably transformed by adaptation to extremely small size. The miniaturization-related changes in the complex multimodal sense organs of the antennae are of special interest in this context. Scydosella musawasensis (Coleoptera: Ptiliidae) is the smallest free-living insect, with a body length of the smallest measured specimens only 325 μm. We have studied the antennal sensilla of S. musawasensis using scanning electron microscopy and described their sizes, external morphological features, and distribution. Eight different morphological types of sensilla have been revealed: sensilla chaetica, four types of sensilla trichodea, sensilla styloconica, and two types of sensilla basiconica. The numbers of sensilla of all types are identical in males and females. Comparative analysis with the available published data on the larger Coleoptera has revealed a decrease in the number of antennal sensilla with decreasing body size; S. musawasensis has only 124 sensilla per antenna. The revealed size-related trends in free-living insects have been compared with those determined earlier in the miniature parasitoid waspsMegaphragma spp. (Hymenoptera: Trichogrammatidae), which have a body size of about 200 μm. S. musawasensis has three times as many antennal sensilla as Megaphragma wasps, which demonstrate pronounced sexual dimorphism in the numbers and types of these sensilla. Our data contributes to the morphological, functional and evolutionary context needed for understanding the effects of miniaturization on the structure of the brain and sensory organs of microinsects. Together with our earlier data, the results of this study reveal the universal principles of antennal miniaturization: extreme level of optimization combined with retention of high functionality of the antennal sensory system. This study was supported by the Russian Foundation for Basic Research (project no. 19-34-90162).