Ciliophora
Classification systems

The first comprehensive system of ciliate classification was proposed by Bütschli (1887-1889) in the late 19th century. He, like Kahl (1930-1935) who replaced his system about 50 years later, used mainly the type and variation in the oral and somatic ciliature as main characters for distinguishing higher taxa. Subsequent systems have changed more rapidly. In the mid-20th century, after silver impregnation methods became popular, the scheme was revised e.g., by Fauré-Fremiet (1950-1970) using infraciliary and morphogenetic data. Fauré-Fremiet's scheme of the ciliates was later adopted by Honigberg et al. (1964) in their major revision of all protozoa.

Since the beginning of the 1970's, morphogenetic criteria, particularly the formation of the oral apparatus, and ultrastructural data were employed increasingly to distinguish higher categories. De Puytorac et al. (1974), for instance, used mainly the fine structure of the oral area to construct a system. A more comprehensive set of characters was utilized by Corliss (1979) in a subsequent attempt, which gained widespread recognition. With a growing number of taxa, more available ultrastructural data, and recognition of increased ciliate diversity, the classification had to be altered again. Consequently, the schemes provided e.g., by Levine et al. (1980), Small and Lynn (1985, who used mainly the structure of the somatic kinetid), de Puytorac et al. (1987), or de Puytorac (1994) introduced many new higher taxa, elevated existing groups to higher ranks, and transferred others to far distant categories.

In modern systems, a combination of characters, like details of the somatic and oral infraciliature, fine structure of the cortex, stomatogenesis and other morphogenetical features, macronuclear characteristics, life cycle information and, if available, molecular biological data (e.g., subunit rRNA sequences), are used in reconstructing phylogenetic trees. But even the latest classifications may be regarded only as transient and are likely to change again shortly.

The illustrated glossary of terms widely used for describing ciliates is based mainly on compilations by Corliss (1979), Corliss and Lom (1985), Foissner et al. (1995), and Foissner and Dragesco (1996a).