Based mainly on:
Kulda, J. and Nohynkova, E. (1978). Intestinal Flagellates. Parasitic protozoa II (Kreier, J.P., ed.) Academic P, Inc., New York, 2-139
Dyer, B.D. (1989). Phylum Zoomastigina Class Pyrsonymphida. Handbook of Protoctista (Margulis, L., ed.), Johnes and Bartlett Publishers, Boston, 266-269
This order consists of two groups. Various authors regard them as separate taxons on different taxonomic level and not regard them as relative groups.
The family Polymastigidae include primitive oxymonads predominantly living in insects. members of the genus Monocercomonoides inhabit also the intestine of vertebrates. None of them is pathogenic. Although the occurrence of both trophozoites and cysts appears to be a general feature in the genus Monocercomonoides, only the trophozoite stage has been described for the majority of species. The cysts reported in some species from insects are round, uninucleate, and have a thin wall. Trophozoites of the genus Monocercomonoides have a round or ovoid body equipped with four flagella arranged in two separate pairs. All flagella are of the acroneme type , e.g., terminated by a thin filament. One or more flagella are recurrent adhering to the body for some distance, and then continuing in free trailing portion. Each recurrent flagellum is accompanied by a ribbon of funis which follows and, sometimes , surmounts the adherent part of the flagellum. Two separate groups of kinetosomes are connected by U-shaped fiber. One group is placed dorsally, the other ventrally in the frontal part of the body. The axostyle, joined to the dorsal group of kinetosomes, extends posteriorly where it often projects for a short distance. Its uniform thickness throughout its length is typical feature. The apex of the body is enveloped by a large pelta. Beneath the pelta is a helmet-shaped body-preaxostyle-capping the anterior pole of the nucleus. The anteriorad situated nucleus of vesicular type is round and typically contains a large spherical endosome. Conspicuous digestive vacuoles with food particles are numerous in the cytoplasm. Trophozoites of the genus Monocercomonoides multiply by binary fission. No multiplication in the cyst stage has been observed.
The pyrsonymphids are heterotrophic protists that have been found only in the hindgut of wood-eating cock-roaches and termites. They have been placed in the separate class pyrsonymphida by Margulis and Schwartz (1988). This group contains genera Notilla, Oxymonas, Pyrsonympha , Saccinobaculus etc. Pyrsonymphids are characterised by the presence of 4, 8, or 12 flagella and motile axostyle that extends the length of the body. Hydrogenosomes and mitochondria have not been detected in pyrsonymphids. Many bacteria including spirochetes, can be associated with pyrsonymphids as epi- and endosymbionts. Pyrsonymphides are of indirect practical importance by their obligate association with their wood-destroying hosts, the dry wood and subterranean termites. Pyrsonymphids have complicated life cycle with meiosis and gametes involved.
Fig. 2. TEM analytical drawing of Pyrsonympha vertens . Axostyle(A), cytostome (C), endosymbiotic bacteria (E), nucleus (N), symbiotic spirochetes (S), flagella(U), wood particle (W). (Drawing by Christie Lyons. Reprinted from Margulis , L. and Sagan, 1986, Origin of Sex, Yale University Press).