An order of the protozoan class Myxosporidea (subphylum Cnidospora). It is characterized by the production of trivalved spores with three polar capsules and one to many sporoplasms. The spore membrane may be extended into anchor-shaped processes, which may have bifurcate tips. These protozoan parasites are found in the body cavity or in the intestinal lining of fresh-water annelids and in marine worms of the phylum Sipunculoidea.