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contractile protein filaments in the cytoplasm of protozoans, generally in the superficial layers of the body. They may be smooth or striated and, like myofibrils, they possess double refraction. They consist of dozens or, more often, hundreds of fibrils from 3 to 25 nanometers in diameter. The contraction and thickening of the myonemes alter the shape of a protozoan’s body or part of it, such as the tentacles or the gullet.