Terrestrial isopods are unique among crustaceans, having conquered diverse terrestrial habitats. Comparing to aquatic isopods, they have a great variety of structures on their dorsal cuticle. Isopods Porcellionides pruinosus are covered with spherical microstructures that give this species a frosted look. The purpose of this master thesis was to determine the structure, composition, optical properties and mechanism of formation of these spherical microstructures. Using a variety of microscopy techniques, we were able to visualize the cuticle surface of pereon tergites. The composition of spheres was determined with histological stains and comparison of tergites treated with chemicals using scanning electron microscopy (SEM). The refractive index of the spheres was determined by the immersion of tergites in chemicals with different refractive indices and observing them with phase contrast and differential interference contrast (DIC). The formation of spheres was studied during the moult cycle and the formation of the cuticle and cuticular structures were observed with DIC, fluorescent
microscopy, SEM and transmission electron microscopy (TEM). The spheres were found to be composed of basic macromolecules, most likely polysaccharides or glycosylated proteins. The spheres are transparent with
structured surface and have a refractive index of 1.53, which is similar to the refractive index of glass. The spheres are formed in the premolt phase, when the
epicuticle is generally formed. The epidermal cells form cell extensions that secrete electron-dense substance that could represent the building blocks of spheres. The spheres are not homogeneously composed and change their appearance when the connection with epidermal cells via stems is broken. The evolutionary advantage of these structures is still unknown.