Description of Trichomonadida

Flagellates generally with three to five anteriorly directed flagella and a recurrent one forming an undulating membrane; in Dientamoeba, basal bodies and flagella are absent; with a parabasal apparatus composed of two parabasal fibres supporting one or two dictyosomes which are sometimes very long and in several Devescovinidae are twisted around the axostyle; the axostyle-pelta complex occupies the central axis of the cell and generally protrudes at the posterior end; however, some genera have a reduced (Histomonas) or no axostyle (Dientamoeba), and in Pentatrichomonoides the axostylar row of microtubules is peripheral; axostyle forms a tube-like trunk which tapers and protrudes posteriorly and has an anterior capitulum, which is spoon-shaped and cups the surface of the nucleus; hydrogenosomes are spherical or bacilliform granules which concentrate around the axostyle and under the costa; division by pleuromitosis where the paradesmose is the major distinguishable structure; with various striated roots attached to the basal bodies, the parabasal fibres are present in all species, and the costa is generally present in genera which have an undulating membrane, i.e. the Trichomonadidae; two types of Undulating membranes; rail-type where the recurrent flagellum adheres to the top of an elevation of the cell surface; and lamellar-type which adheres laterally to a lamellar elevation of the cell surface; a third type of modification of the recurrent flagellum occurs in Devescovinidae, where the cord-like or ribbon-like recurrent flagellum contains a bundle of microfibrils associated with the axoneme, adheres to the cell body surface where it is underlain by a dense fibrous structure named the cresta; length of the cresta and of the adhering portion is variable depending upon the species.