They are often categorized according to the principle organ system they invade: Clonorchis sinensis, Fasciola hepatica, and Opisthorchis species: Liver and bile ducts Fasciolopsis buski, Heterophyes heterophyes, and related organisms: Lumen of the gastrointestinal tract Paragonimus westermani and related species: Lungs Schistosoma species: Vasculature of the gastrointestinal or genitourinary system