Parabasalids
Parabasalids also have reduced mitochondria; called hydrogenosomes, these organelles generate some energy anaerobically, releasing hydrogen gas as a by-product. The best-known parabasalid is Trichomonas vaginalis, a sexually transmitted parasite that infects some 5 million people each year. T. vaginalis travels along the mucus-coated lining of the human reproductive and urinary tracts by moving its flagella and by undulating part of its plasma membrane. In females, if the vagina's normal acidity is disturbed, T. vaginalis can outcompete beneficial also can occur in the uretha of males, though often without symptoms.