Holotrichs are ciliate protozoa that have relatively uniform cilia over their body, and lack or only have a few prominent oral membranelles. Most of the major lines of ciliates are holotrichous. They do not form a natural group, so the term is now used only as a physical description, although it has appeared in many earlier classifications. They were one of two orders in the classification of ciliates introduced by Otto Bütschli in 1889:

Class Ciliata
    Order Holotricha
       Suborder Gymnostomata
       Suborder Trichostomata
       Suborder Astomata
    Order Spirotricha
       Suborder Heterotricha
       Suborder Oligotricha
       Suborder Hypotricha
       Suborder Peritricha

In this system the spirotrichs included all ciliates that have prominent oral cilia, and the holotrichs all those that lack them. Later the peritrichs, as well as the chonotrichs , were either given their own groups or considered unusual holotrichs. In 1974, de Puytorac and various other workers abandoned the holotrichs, dividing them into the classes Oligohymenophorea and Kinetofragmophora. The latter have since been divided into several more classes, and the gymnostomes in particular have been split into several different groups.