Family Monocercomonadidae

This family, like the Trichomonadidae, belongs to the order Trichomonadorida. Its members have either a free or adherent trailing flagellum, but lack the undulating membrane and costa found in the Trichomonadidae. Four genera, Monocercomonas, Hexamastix, Protrichomonas and Chilomitus, occur in the intestinal tracts of domestic animals.

Genus Monocercomonas

In this genus the body is piriform, with a rounded anterior end. There is a pelta. The cytostome and nucleus are anterior. There are 3 anterior flagella and a trailing one. The axostyle projects beyond the posterior end of the body. Travis (1932) showed that Trichomastix Blochmann, 1884 and Eutrichomastix Kofoid and Swezy, 1915 are synonyms of Monocercomonas. Morgan (1944) gave a checklist of species of the genus; it included 20 species, of which 4 were from mammals, 4 from birds, 2 from reptiles, 1 from amphibia, 2 from fish and 7 from insects and other arthropods. Others have been described since.


Monocercomonas ruminantium (Braune, 1914) nov. comb, occurs in the rumen of cattle. In addition, Morgan and Noland (1943) found what was probably the same organism in material from the sheath of bulls.

The body is about 8 u long, with 3 anterior flagella about 8 u long and a trailing flagellum a little longer. The axostyle is curved and does not extend beyond the body, altho the posterior end is pointed. A line of granules runs beside the convex side of the axostyle. This species is non-pathogenic, but must be distinguished from Tritrichomonas foetus.

Synonyms of this species are Trichomonas ruminantium Braune, 1914; Tricercomitus ruminantium (Braune, 1914) Christl, 1954; and Tritrichomonas ruminantium (Braune, 1914); but not Trichomastix ruminantium Braune, 1914. Altho Braune (1914) assigned this species to the genus Trichomonas and succeeding workers have followed him in this or at the most have changed the generic name of Tritrichomonas, Christl (1954) pointed out that the absence of an undulating membrane made this assignment incorrect. Christl transferred it to the genus Tricercomitus, but it belongs more properly to the genus Monocercomonas.

Monocercomonas cuniculi (Tanabe, 1926) occurs in the cecum of the domestic rabbit. It is piriform, 5 to 14 u long. Its axostyle is slender, hyaline, and projects from the body.

Monocercomonas gallinarum (Martin and Robertson, 1911) Morgan and Hawkins, 1948 is said to occur in the ceca of the chicken. Kotlan (1923) reported it from a single domestic duck. Its body is piriform, 5 to 8 by 3 to 4 u. There is some question whether this is a valid species. It has been reported by Martin and Robertson (1911) in England, Kotlan (1923) in Hungary, and Morgan and Hawkins (1952) in Wisconsin, but McDowell (1953) failed to find it in 1000 slides from a large number of chickens in Pennsylvania. McDowell believed, along with Minchin (1917), Wenyon (1926), Doflein and Reichenow (1929) and others, that it is simply a degenerate Trichomonas eberthi.

Genus Hexamastix

In this genus the body is piriform, with a rounded anterior end. The cytostome and nucleus are anterior. There are 6 flagella, of which 1 trails. (According to Nie, 1950, the number of anterior flagella varies in this genus from 2 to 6.) A pelta is present, the axostyle is conspicuous, and the parabasal body prominent. Members of this genus have been found in mammals, amphibia and insects. Hexamastix caviae Nie, 1950 and H. robustus Nie, 1950 occur in the guinea pig cecum, and H. muris (Wenrich, 1924) in the cecum of the Norway rat, golden hamster and other rodents.

Genus Chilomitus

The body is elongate, with a convex aboral surface. The pellicle is well developed. The cuplike cytostome is near the anterior end. Four flagella emerge thru it from a bilobed blepharoplast. The nucleus and parabasal body are just below the cytostome. An axostyle is present but may be rudimentary. Cysts may occur. Only a few species have been described, all in mammals. Chilomitus caviae da Fonseca, 1915 and C. conexus Nie, 1950 occur in the guinea pig cecum.

Genus Protrichomonas

The body is piriform or beet-shaped, with 3 anterior flagella of equal length arising from an anterior blepharoplast, an anterior nucleus and an axostyle. Three species have been named, from birds, mammals and a fish.

Protrichomonas ruminantium (Braune, 1914) novo comb, was originally assigned by Braune (1914) to the genus Trichomastix (now Monocercomonas), but the absence of a trailing flagellum makes this assignment incorrect. Its description agrees with that of Protrichomonas, altho it must be said that this genus is badly in need of redescription. P. ruminantium occurs in the rumen of cattle and sheep. It is about 8 u long. Its nucleus is often surrounded by a clear zone. No cytostome was seen.

Protrichomonas anatis Kotlan, 1923 has been described from the large intestine of the domestic duck and other water birds. It is 10 to 13 u long and 4 to 6 u wide. Two distinct fibrillae arise from the anterior blepharoplast and pass back thru the body, separating to pass around the nucleus and finally passing out of the body as a pointed axostyle. The nucleus is often triangular.

Order Polymastigorida

Members of this group have 2 to about 12 flagella and 1, 2 or several nuclei. They lack a costa, axostyle (except in some Hexamitidae and Polymastigidae) and parabasal body.