English: A crystal water flea (Sida crystallina) photographed under a microscope using an 8x objective and dark-field microscopy. The specimen was collected from Lake Neeruti in Lääne-Viru County, Estonia, in June 2022. This is one of the largest and most common littoral cladocerans in our water bodies. The image clearly shows the species' characteristic rectangular transparent body and large ventrally positioned compound eye, which glows distinctively orange under dark-field illumination. Two developing embryos can be seen in the dorsal brood pouch, identifiable by their dark eyes. Through the transparent carapace, yellowish-green structures are also visible. The image was captured using dark-field microscopy, where light rays are directed at the specimen from the sides using a special condenser so that no direct light reaches the objective lens. In the microscope, we only see the light that is reflected or scattered by the specimen. This technique particularly emphasizes the contours and internal structures of transparent objects, creating a bright image against a dark background. The image was created using focus stacking technique, which ensures great depth of field throughout the subject.