Like most anaerobic ciliates, armophoreans have mitochondria-derived organelles called hydrogenosomes. These specialized organelles produce energy for the cell in absence of oxygen by the fermentation of pyruvate into acetate and hydrogen. Armophoreans harbor methanogenic endosymbiotic archaea that have been located in the cytoplasm adjacent to their hydrogenosomes. Host cells can contain up to 10,000 methanogens, and they are thought to play roles in host growth and metabolism. It is hypothesized that these symbionts consume the hydrogen that is produced as an end-product of fermentation, making it a more favorable reaction and increasing its energetic yield. Marine armophoreans also harbor ectosymbiotic bacteria that are sulfate reducers, which are thought to play a similar role as the endosymbiotic methanogens in that they also consume hydrogen as a metabolite of host fermentation.
