An order of protozoa in the class Myxosporidea (subphylum Cnidospora). It is characterized by production of spores with a relatively thick, single intrasporal filament and three uninucleate sporoplasms. The spore membrane occurs as a single piece. Helicosporidium parasiticum is the only species in the order. The parasite infests the body cavity, fat bodies, and ganglia of mites (Hericia hericia) and the body cavity of fly larvae (Dasyhelea obscura and Mycetobia pallipes) found in the sap of horse chestnut and elm trees.