LAUSR

The nature of retinal shielding pigment in the larv al eyes of the midge Clunio marinus was studied by high resolution scanning X-ray fluorescence (XRF) a nalysis correlated with light microscopy and scanning coherent X-ray diffractive imaging (Ptycho graphy). Clunio is known as a unique model system to decipher mechanisms underlying the complex moonrelated rhythms. Shielding pigment granules within the photoreceptor cells of their primitive e yes (ocelli) have been shown to change appearance i n the same rhythm [1]. The larvae are equipped with s imple pigment-cup eyes (ocelli) in which the dense shielding pigment permits light access to the photo sensitive rhabdomers only through a narrow pinhole resulting in a diffuse image of the environment. Th e pigment cup of these eyes becomes transparent during full moon [2]. Within the photoreceptor cell s of the ocelli, melanin containing melanosomes for m shielding pigment granules. Melanin is a nearly uni versally occurring pigment in different organisms and organ systems with several known functions; not o ly as shield against bright light (especially UV light), but also as reservoir or sink of excessive amounts of metals, and as a component of the immune system [3]. Trace metals have been shown to be indi cators of certain steps of melanogenesis. The aim o f this study is to combine different non-destructive microscopy techniques to analyse the process of melanogenesis with single melanin granule-resolutio n.