A specialized eukaryotic organelle that consists of a filiform extrusion of the cell surface and of some cytoplasmic parts. Each cilium is largely bounded by an extrusion of the cytoplasmic (plasma) membrane, and contains a regular longitudinal array of microtubules, anchored to a basal body. The longitudinal array of microtubules are almost always in a 9+2 array with 2 microtubles in the central cilia bundle and 9 sets of doublet microtubules around the perimeter. The exception to this arrangement is spermatazoa flagella, which have a 9+1 array in planarians. [ ]

A specialized eukaryotic organelle that consists of a filiform extrusion of the cell surface and of some cytoplasmic parts. Each cilium is largely bounded by an extrusion of the cytoplasmic (plasma) membrane, and contains a regular longitudinal array of microtubules, anchored to a basal body. The longitudinal array of microtubules are almost always in a 9+2 array with 2 microtubles in the central cilia bundle and 9 sets of doublet microtubules around the perimeter. The exception to this arrangement is spermatazoa flagella, which have a 9+1 array in planarians. [ http://amigo.geneontology.org/amigo/term/GO:0005929 ]