Contractile vacuole is absent in Entamoeba because the medium around it (in host's colon) is isotgpic to its cytoplasm, so there is no need of osmoregulation. Amoeba which lives in freshwater has contractile vacuole. Since freshwater is hyptotonic to cytoplasm of Amoeba, there is continuous endosomosis or inflow of water into the body. Also, some water is added to the cytoplasm from food vacuole and from catabolic reactions. If all this water is allowed to accumulate, the body will soon swell up and burst. So all freshwater protozoan including Amoeba possess contractile vacuole to eliminate excess water from the body which is known as osmoregulation. Pseudopodia are present in trophic form of Entamoeba.