Question

which are the five fresh water protozoan​

Answer 1

Protozoan organisms are usually single-celled and heterotrophic (using organic carbon as a source of energy), belonging to kingdom Protista. They live in a wide variety of moist habitats including freshwater, marine environments, and the soil.

Examples for freshwater shelled protozoans include Arcella and Difflugia.

They both produce shells(or tests) from mineral particles.

Answer 2

Answer:

Fresh water protozoans live in hypotonic solution so, for regulation of excess of water which comes in the protoplasm through the process of endosmosis, contractile vacuoles have developed, When these protozoans are placed in marine water i.e., hypertonic water, the contractile vacuoles become disappear