An actin-based protrusion from the apical surface of auditory and vestibular hair cells and of neuromast cells. These protrusions are supported by a bundle of cross-linked actin filaments (an actin cable), oriented such that the plus (barbed) ends are at the tip of the protrusion, capped by a tip complex which bridges to the plasma. Bundles of stereocilia act as mechanosensory organelles. [ http://www.ncbi.nlm.nih.gov/pubmed/15661519 http://www.ncbi.nlm.nih.gov/pubmed/7840137 ]