metopus rex metopus rex metopus rex is a species of metopid first found in soil from the murray river floodplain, australia. this species can be distinguished from its congeners by its large body size and the shape of the macronucleus. m. rex exhibits up to 30μm-long endosymbiotic bacteria. metopus rex scientific classification domain: eukaryota (unranked): sar (unranked): alveolata phylum: ciliophora subphylum: intramacronucleata order: armophorida family: metopidae genus: metopus species: m. rex binomial name metopus rexvďačný & foissner, 2016