The monophylum oxytrichidae (ciliophora, hypotrichia) contains freshwater-, marine-, and soil-dwelling species. Some taxa are extremely widespread in freshwater, such as oxytricha, stylonychia or in terrestrial habitats. Oxytricha and stylonychia have been used for many molecular, ultrastructural, and genetic investigations. This book summarizes the morphological, morphogenetic, faunistic, and ecological data from the past 220 years, scattered in more than 2500 references from all over the world. One central dichotomous key leads directly to 32 genera comprising about 169 species, which are illustrated by more than 2400 figures, including original ones. Taxonomists, ecologists, limnologists, soil biologists, and cell biologists will find a list of synonyms, a discussion of nomenclatural and taxonomic problems, and a detailed morphological and ecological description, including almost all published faunistic records. This enables both the specialist and the practitioner to determine species without referring back to the original literature. The book offers the interested scientist a thorough and up-to-date revision of the oxytrichids.