Population and developmental genetics represent the two most prominent approaches of modern evolutionary research. Within the field of evolutionary developmental biology (EvoDevo), the evolutionary developmental genetics approach gained importance due to progress in the cloning and visualization techniques. Today a fusion of classical population genetics and developmental genetic data seems both challenging and necessary. On the way towards synthetic interpretations and evaluations of evolutionary scenarios there is a need for model systems that are well investigated both regards. The bodyplans of higher Crustacea (Malacostraca) may present such a model system. Studies on Malacostracan development have shown that there is a strong correlation between the expression patterns of the trunk Hox genes Antp, Ubx and abd-A and the realized bodyplan in regard to tagmatization. Malacostracan population genetics has also been the subject of numerous investigations, and complex mating systems seem to be present in various different Malacostracan taxa (Amphipoda, Isopoda, Decapoda). In my doctoral thesis I will introduce and test a number of hypotheses that implicate complex mating systems and their population genetic consequences, as key factors in the evolution of Malacostracan bodyplans. Sexual selection in particular is assumed to act directly on the expression patterns of developmental regulatory genes underlying the morphology of structures that are crucial for the mating behavior. Therefore the main aim of this work is a detailed investigation of the complex mating system of Dikerogammarus villosus (Sowinski, 1894; Malacostraca, Amphipoda, Gammaridae) in terms of phenotypic integration, using modern and innovative techniques like x-ray microCT for acquiring morphometric data. Besides morphometric measurements, antibody staining will be performed to reveal the expression of Ubx during the development of trunk appendages in different gammarid species. Based on the combination of morphometric and genetic data, this research may yield new insights on the mechanisms of Malacostracan bodyplan and appendage evolution.