The Oligohymenophorea are a large class of ciliate protozoa. There is typically a ventral groove containing the mouth and distinct oral cilia, separate from those of the body. These include a paroral membrane to the right of the mouth and membranelles, usually three in number, to its left. The cytopharynx is inconspicuous and never forms the complex cyrtos found in similar classes. Body cilia generally arise from monokinetids, with dikinetids occurring in limited distribution over part of the body. Classes Karyorelictea Heterotrichea Spirotrichea Litostomatea Phyllopharyngea Nassophorea Colpodea Prostomatea Oligohymenophorea Plagiopylea See text for subclasses. ...

In most groups the body cilia are uniform and often dense, while the oral cilia are inconspicuous and sometimes reduced, but among the peritrichs almost the opposite is the case. Members are widely distributed, and include many free-living (typically fresh-water, but many marine) and symbiotic forms. Most are microphagous, grazing on smaller organisms swept into the mouth by the cilia, but various other feeding habits occur. In one group, the astomes, the mouth and associated structures have been lost altogether. Typical orders Sessilida Mobilida The peritrichs are a large and distinctive group of ciliate protozoa. ... Families Anoplophryidae Archiastomatidae Clausilocolidae Contophryidae Haptophryidae Hoplitophryidae Intoshellinidae Maupasellidae Radiophryidae Astomes (order Astomatida) are a group of uniformly ciliated protozoans commonly found in the guts of annelid worms, especially oligochaetes, and other invertebrates. ...

The Oligoohymenophorea were first proposed in 1974 as one of three classes of ciliates, together with the Polyhymenophorea or spirotrichs and the now abandoned Kinetofragmophora. Since then the apostomes have been added, but otherwise its composition has remained relatively constant, with the main variations being the positions of the peniculids and plagiopylids. Typical sublasses Subclass Hypotrichia Subclass Stichotrichia Subclass Oligotrichia Subclass Choreotrichia The spirotrichs are a large and distinctive group of ciliate protozoa. ... Holotrichs are ciliate protozoa that have relatively uniform cilia over their body, and lack or only have a few prominent oral membranelles. ... Typical families Suborder Frontoniina     Clathrostomatidae     Frontoniidae     Lembadionidae     Maritujidae     Stokesiidae Suborder Parameciina     Parameciidae     Neobursaridiidae     Urocentridae The peniculids are an order of ciliate protozoa, including the well-known Paramecium and its close relatives. ... Typical families Plagiopylidae Sonderidae The plagiopylids are a small order of ciliate protozoa, including a few forms common in anaerobic habitats. ...

References

• Puytorac, P. de, A. Batisse, J. Bohatier; J.O. Corliss, G. Deroux, P. Didier; J. Dragesco, G. Fryd-Versavel, J. Grain, C.-A. Grolière, R. Hovasse, F. Iftode, M. Laval, M. Rogue, A. Savoie, and M. Tuffrau. (1974). Proposition d'une classification du phylum Ciliophora Doflein, 1901. Comptes Rendus de l'Académie de Sciences, Paris 278: 2799-2802.