The Holotrich Ciliates

Abstract

Holotrich ciliate protozoa have been observed frequently in samples obtained from the principal fermentative regions in the digestive tracts of herbivorous mammals. The descriptive term “holotrich” initially arose from the terminology used in the original major systems of protozoal classification. Prior to the taxonomic revisions of Levine et al. (1980), the families of holotrich ciliates were classified in two orders of the subclass Holotrichia; the entodiniomorphid (oligotrich) ciliates were classified in the order Entodiniomorphida (Corliss, 1979). In subsequent revisions the order Entodiniomorphida has been retained while the subclass Holotrichia has been superceded (see Section 3.1), although the term holotrich is still widely used for collective description of fifteen genera of ciliates that are classified within two separate taxonomic orders. The classification of the rumen holotrich ciliates is summarized in the following section; subsequent sections discuss their occurrence and morphological characteristics. The term holotrich has been retained here because of its current widespread usage in the literature; the limitations of its use with this diverse group of ciliates should, however, be recognized.