A cell organelle found in certain protists and chytrid fungi that live in anaerobic environments, such as Trichomonas vaginalis, a sexually transmitted parasite of the human reproductive and urinary tracts. Hydrogenosomes typically generate hydrogen as a by-product of ATP production; they are thought to be derived from mitochondria and like them are bounded by a double membrane. However, they lack many of the enzymes required for aerobic respiration, such as an electron transport chain.