The hymenostomes are an order of ciliate protozoa. Most are free-living in freshwater, such as the commonly studied genus Tetrahymena, but some are parasitic on fish or aquatic invertebrates. Among these is the important species Ichthyopthirius multifiliis, a common cause of death in aquaria and fish farms. Classes & Subclasses Class Karyorelictea Class Heterotrichea (e. ... Species Tetrahymena are ciliate protozoa, common in aquatic habitats. ... Ichthyopthirius multifiliis is a species of ciliate protozoa which parasitizes freshwater fish. ... There is also a Russian band named Aquarium, and Aquarium is the name of an album by the Danish pop-dance group Aqua A 335,000 US gallon (1. ... A demonstration aquaculture facility Fish farming is the principal form of aquaculture. ...

The hymenostomes are fairly typical members of the Oligohymenophorea. Their body cilia are mostly uniform, sometimes with a few long caudal cilia, and arise from monokinetids or from dikinetids at the anterior. The oral cilia are in general distincly tetrahymenal, with three membranelles and a paroral membrane, which corresponds only to the middle segment of the tripartite membranes found in certain scuticociliates. Mouth formation during cell division usually begins next to a postoral kinety. Typical orders Subclass Peniculia     Peniculida Subclass Hymenostomatia     Hymenostomatida Subclass Scuticociliatia     Philasterida     Pleuronematida     Thigmotrichida Subclass Astomatia     Astomatida Subclass Apostomatia     Apostomatida     Astomatophorida     Pilisuctorida Subclass Peritrichia     Sessilida     Mobilida The Oligohymenophorea are a large class of ciliate protozoa. ...

The hymenostomes were first defined by Delage & Hérouard in 1896. Initially the scuticociliates and peniculids were included, then later treated as separate orders of a subclass Hymenostomatia, to which the astomes are sometimes added. More recently each of these groups tends to be treated as a separate subclass. 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. ...