Contractile vacuoles

Contractile vacuoles are found in free-living freshwater nonphotosynthetic protistans. Their function is to regulate osmotic pressure within the cell by expelling water from a central vacuole through a pore in the outer surface. The  simplest contractile vacuoles consist of a vacuole that can  form  anywhere in the  cell, to a fixed structure that is surrounded by bands of microtubules and  surrounded by collecting canals that collect fluid from the cytoplasm.

                                         Figure: Diagram of a contractile vacuole