A short minute hairlike structure (up to 10 μm long) present on the surface of many cells, notably in certain protozoans and some types of vertebrate epithelium. Cilia usually occur in large groups and are shorter than eukaryotic flagella, although both organelles have the same structure and are collectively termed undulipodia (see undulipodium). Beating of cilia can produce cell movement or create a current in fluid surrounding a cell. See also axoneme.
http://www.cytochemistry.net/Cell-biology/cilia.htm Details of the ultrastructure of cilia and flagella
Subjects: Biological Sciences.