Why sporozoans donot have contractile vacuole even though most of protozoans have contractile vacuole?

Marine protozoa do not have contractile vacuole unlike fresh water protozoa because of the reason that contractile vacuole is used to store and remove excess water (due to endosmosis) which if comes in rapidly can cause the cell to burst,As marine protozoa have a hypertonic external enviorment they do not possess a problem of excess endosmosis instead they have to conserve their water content from getting lost in enviorment.