Which of the following class of protozoa does not generally contain contractile vacuole?

The correct answer is Sporozoa.

To understand why protozoans in the class Sporozoa generally lack contractile vacuoles, let us look at the function of a contractile vacuole and the lifestyle of sporozoans:
1. Function of Contractile Vacuole: The primary function of a contractile vacuole is osmoregulation. It helps in pumping excess water out of the cell to prevent the protozoan from swelling and bursting. This organelle is essential for free-living freshwater protozoans (such as amoebae in Rhizopoda, paramecia in Ciliata, or certain flagellates in Flagellata) because freshwater is hypotonic compared to their cytoplasm, causing water to continuously enter their cells via osmosis.
2. Lifestyle of Sporozoans: Sporozoans are a class of parasitic protozoa (e.g., Plasmodium, which causes malaria). They live inside the bodies of hosts (endoparasites) where the environment (blood, tissue fluids, or cells) is isotonic to their cytoplasm. Since there is no net influx of water, there is no need for osmoregulation, and therefore, contractile vacuoles are absent in them.