Ciliophora, or ciliates, are a group of protists that utilize cilia for locomotion. Examples include "Paramecium", "Stentors", and "Vorticella". Ciliates are widely abundant in almost all environments where water can be found, and the cilia beat rhythmically in order to propel the organism. Many ciliates have trichocysts, which are spear-like organelles that can be discharged to catch prey, anchor themselves, or for defense. Ciliates are also capable of sexual reproduction, and utilize two nuclei unique to ciliates: a macronucleus for normal metabolic control and a separate micronucleus that undergoes meiosis. Examples of such ciliates are "Paramecium" and "Tetrahymena" that likely employ meiotic recombination for repairing DNA damage acquired under stressful conditions.