Amoeba contains cytoplasm, which is differentiated into outer plasma membranes. The cytoplasm contains food vacuoles, a nucleus, and a contractile vacuole. The amoeba has no mouth or anus. During adverse environment, amoebas survive by encystment: the amoeba becomes circular, loses most of its water, and its pseudopodia then secretes a cyst membrane that serves as a protective covering. When the environment is again suitable, the envelope ruptures.