Which of the following is not a characteristic feature of prtozoans

To determine which of the given options is not a characteristic feature of protozoans, let us analyze each option step-by-step:

1. Binary Fission: Binary fission is a very common method of asexual reproduction in protozoans, where a single parent cell divides into two approximately equal daughter cells. Examples include Amoeba and Paramecium. Thus, this is a characteristic feature.

2. Pseudopodia: Pseudopodia (temporary cell extensions or "false feet") are characteristic locomotory and feeding structures in sarcodines (amoeboid protozoans). Thus, this is a characteristic feature.

3. Contractile Vacuole: A contractile vacuole is an essential organelle present in many freshwater protozoans (like Amoeba and Paramecium) responsible for osmoregulation (regulating water balance) and excretion. Thus, this is a characteristic feature.

4. Cell membrane as an outer body covering: While protozoans are eukaryotic single-celled organisms, a simple cell membrane is not the definitive or universal outer body covering for all of them. Many protozoans possess a specialized, firm but flexible outer layer called a pellicle (e.g., in ciliates like Paramecium and flagellates like Euglena) or even hard shells/tests made of silica or calcium carbonate (e.g., in radiolarians and foraminiferans). Therefore, having a simple cell membrane as the sole outer body covering is not a uniform characteristic feature of all protozoans.

Hence, the option that is not a characteristic feature of protozoans is "cell membrane as an outer body covering".