The Phylum Protozoa is divided into four classes on the basis of their
A. Nuclear structure
B. Locomotory structure
C. Mode of reproduction
D. Mode of nutrition

Hint: Euglena, Amoeba, Plasmodium, Paramecium, Podophyllum a few examples of Phylum Protozoa. Approximately, 50,000 types of Phylum Protozoa have been identified. Its four divisions are Amoeboid Protozoa or Sarcodines, Flagellated protozoans or Zooflagellates, Ciliated protozoa or Ciliates and the Sporozoans.

Complete Answer:
- The protozoans are basically eukaryotes (cells having nucleus enclosed by a nuclear envelope). The basic nuclear structure of the different types of Phylum Protozoa is quite similar.Hence, nuclear structure cannot be the basis of classification in Phylum Protozoa.
- Binary fission is the most common means of asexual reproduction among the protozoans. Other means of reproduction include budding and schizogony. But, most of them use the same modes of reproduction. Hence, this option is also not correct.
- The modes of nutrition in protozoa are Holozoic (ingestion), Saprozoic (osmosis) and Parasitic (feeding). But, most of their subgroups use the same modes of nutrition. So, this answer is not correct.
- The varied species of protozoa show distinct types of locomotion. The Sarcodines (the largest Phylum) exhibit Amoeboid movement whereas flagellar movement is characterized by Zooflagellates. Hence, we can say that on the basis of their locomotory structure, the Phylum Protozoa is divided into four classes or groups.

Hence the correct answer is option ‘B’.

Note: There is great diversity in the Phylum Protozoaregarding their modes of reproduction, nutrition and other specifications. All of these protozoa are following the Commensalism in their symbiotic habitat. But the only basis of their classification is the Locomotory Structure which is being deployed by them.