A cilium (plural cilia) is an organelle found in eukaryotic cells. Cilia are tail-like projections. There are two types of cilia: motile cilia and non-motile, or primary, cilia, which typically serve as sensory organelles. Along with flagella, they make up a group of organelles known as undulipodia. Types and distribution In animals, cilia are found on epithelial surfaces. Cilia are rare in plants, occurring most notably in cycads. Ciliates are microscopic organisms that possess motile cilia… (More on Cilia)