Archaezoa is composed of two kingdoms of protists, Kingdom Diplomadida and Kingdom Parabasala. These 2 kingdoms are grouped together because they lack mitochondria. The Archaezoa hypothesis suggests that these two kingdoms originally had mitochondria, but lost them before mitochondria became symbionts of protists. This lineage is believed to be the proof of Eukaryotic Endosymbiosis.[by whom?] Molecular evidence indicates that Archaezoa have the genetic marker of mitochondria in their nucleus that suggests they had and then lost mitochondria. Both of these kingdoms are parasites, as they have to acquire ATP from some source. An example of these Archaezoans is Trichomonas vaginalis, a common urinary infection that is transmitted through sexual contact.