Ciliophora. A subphylum of the Protozoa. The ciliates are a fairly homogeneous group of highly differentiated, unicellular organisms. Over 5000 species have been described, and many more surely exist but remain to be discovered. Typically, ciliates are larger than most other protozoans, ranging from 10 to 3000 micrometers (about 1/2500 to 1/8 in.).