sessilida sessilida sessilida is the largest order of the peritrich ciliates. sessilida zoothamnium niveum scientific classification domain: eukaryota (unranked): sar (unranked): alveolata phylum: ciliophora subphylum: intramacronucleata class: oligohymenophorea subclass: peritrichia order: sessilidastein, 1833 families ellobiophryidae epistylididae lagenophryidae operculariidae rovinjellidae scyphidiidae vaginicolidae vorticellidae zoothamniidae list of families ellobiophryidae epistylididae lagenophryidae operculariidae rovinjellidae scyphidiidae vaginicolidae vorticellidae zoothamniidae