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Hymenostome
Delage & Hrouard 1896 Suborder Tetrahymenina
Curimostomatidae
Tetrahymenidae
Turaniellidae
Glaucomidae
Suborder Ophryoglenina
Ichthyopthiriidae
Ophryoglenidae 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, generally with a complicated life-cycle. Among these is the important species Ichthyopthirius multifiliis, a common cause of death in aquaria and fish farms. 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. The hymenostomes were first defined by Delage & Hrouard 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.
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