A marine protozoan is likely to have no contractile vacuole mainly because the cytoplasm is

A marine protozoan is likely to have no contractile vacuole mainly because the cytoplasm is isotonic to seawater. A contractile vacuole is an organelle found in some protozoa that is responsible for regulating the water content of the cell. It does this by pumping excess water out of the cell, which helps the organism maintain its shape and avoid bursting. However, marine protozoa live in an environment where the concentration of salt and other dissolved ions is similar to that of their cytoplasm. This means that they are already in a state of equilibrium with their surroundings and do not need to actively regulate their water content. As a result, marine protozoa are less likely to have a contractile vacuole than freshwater protozoa, which live in an environment that is hypotonic to their cytoplasm and constantly take up water by osmosis.