The ultrastructure and morphogenesis of rhabdites as well as the morphology of pharynx walls in Bothrioplana semperi (Turbellaria, Bothrioplanidae) are described. The ultrastructure of rhabdites and their morphogenesis in this species are close to those in Macrostomida (Turbellaria Archoophora). The order of muscle layers in the pharynx walls of Bothrioplana semperi makes it similar to Tricladida Maricola and some Tricladida Paludicola and Terricola. The analysis of ultrastructural and morphological characters in Bothrioplana semperi as compared to those in Turbellaria Proseriata and Tricladida is provided. It is shown that relation of apomorphic and plesiomorphic characters in the phyla analyzed corresponds the most to the viewpoint about the early divergence of these groups from early Turbellaria Neoophora. In this case Proseriata and Tricladida are not sister groups, while Bothrioplanidae should be regarded as a sister group to the ancestors of Tricladida and, possibly, Neodermata.