An order of parasitic flagellate protozoa belonging to the class Zoomastigophorea. P. P. Grassé suggested that there should be eight orders of these parasitic (and symbiotic) zooflagellates, all in a superorder Metamonadina, but this may be an oversimplification. All retortamonads are medium to large in size and have a complicated blepharoplast-centrosome-axo-style apparatus. Retortamonadida have two or four flagella, one turned ventrally into a cytostomal depression. The nucleus, containing a distinct endosome, is located at the anterior tip. The body is twisted. These organisms are actually symbionts, ingesting bacteria in the digestive tracts of their hosts.