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

Retortamonadida includes only two genera: Retortamonas and Chilomastix. These flagellates are characterised by conspicuous cytostomes and live as comensals in the digestive tract of man, other vertebrate, and various invertebrates. Chilomastix mesnili of man a Chilomastix gallinarum of poultry are suspected of being potentially pathogenic by some authors. Species of both genera can be maintained in agnotobiotic cultures. Their physiology is unknown. Trofozoites of both genera are pyriform, anteriorly rounded, posteriorly elongated and dorsoventrally flattened. Kinetosomes, the vesicular nucleus, and cytostome are located in the anterior part of the cell. The ventrally situated cytostome is the most conspicuous structure. It is formed by a funnellike depression or a groove supported with fibrillar components. The cytopharynx through which food particles enter the cell extends from the bottom of the cytostomal groove. The shape and dimensions of the cytostome as well as the type and arrangement of fibrils associated with it differ in parasites of various genera and species. Four kinetosomes or basal bodies are present in the genera Retortamonas and Chilomastix. The kinetosomes are grouped in two orthogonal pairs. All kinetosomes in Chilomastix are equipped with flagella. In Retortamonas only two kinetosomes posses flagella, the remaining two being barren. One or three flagella are directed anteriorly, providing the cell movement. One flagellum turns posteriorly passing through the cytostomal groove. It is called the recurrent flagellum and is modified by winglike extensions visible under the electron microscope. Surrounding the cell is a layer of subpellicular microtubules, closely apposed to the inner side of the cell membrane. Microtubules also follow the walls of the cytostome and cytopharynx, thus directing the food particles up to the point where endocytosis occurs. In the cytoplasm are numerous food vacuoles and reserve polysaccharide granules. Cisternae of the rough endoplasmic reticulum are located at the cell periphery and around the nucleus. Smooth endoplasmic reticulum has been observed in Chilomastix, with cisternae in spherical configuration the left side beneath the nucleus. There are neither mitochondria nor Golgi apparatus, nor microbodylike organelles in the cells of Retortamonadidae. No microtubular or axial endoskeletal structures of any type are present. Cysts of Retortamonas and Chilomastix are pyriform, lemon-shaped or oval. They are colourless on fresh specimens. Outside the cell membrane they have a thick wall of filamentous material. There is neither operculum nor pore in the cyst wall. All cytoplasmic organelles including flagella, kinetosomes, cytostomal fibrils, etc., with the exception of subpellicular microtubules, are retained inside the cyst.