Ciliate Diversity : Above are shown representatives of four major groups of Ciliata. From left to right, these are Didinium (Litostomatea); Stentor (Spirotrichea); Paramecium (Nassophorea); and Vorticella (Oligohymenophorea).
There are an estimated 7,500 species of ciliate known. Ciliates are classified on the basis of cilia arrangement, position, and ultrastructure. This work now involves electron microscopy and comparative molecular biology to estimate relationships. In the most recent classification of ciliates, the group is divided into eight classes. We list them here, along with common or well-known genera within each class: