Question

Some primitive relatives of animals live as predators or parasites and are divided into four major groups. Elaborate.

Answer 1

Hint: Evolution is a basic law of nature. Ever Since, origin of life, most of the organisms have been evolving in terms of their phenotype and genotype. However, there are some organisms that have not evolved at all and been constant in terms of physical structures. Such organisms are called primitive organisms.

Complete Answer
These primitive relatives of animals, living as a predator and parasites are called protozoans that have been divided into four major groups as follows:
1. Amoeboid protozoans
2. Flagellated protozoans
3. Ciliated protozoans
4. Sporozoans
1. Amoeboid protozoans - live inside freshwater bodies such as sea or moist soil. They are majorly free-living organisms but a few of them are parasites as well. They have pseudopodia as their locomotive structure. The silica shells are also present in some forms.
Examples of amoeboid protozoans are Amoeba and Entamoeba.
2. Flagellated protozoans- The flagellated protozoans are also free-living organisms but sometimes live as parasites. The locomotory structure of flagellated protozoans is flagella. The flagellated protozoans show rare sexual reproduction but diverse types of associations such as parasitic, commensals, symbiont, etc.
The Example of Flagellated protozoans is Trypanosoma.
3. Ciliated protozoans- live mostly inside freshwater and marine water. They can be parasitic. The locomotive structure of ciliated protozoans is Cilia. They possess a definite region of ingestion and egestion. The region of injection is also called the gullet.
An example of ciliated protozoans is Paramecium.
4. Sporozoans- All endoparasites and sporozoans lack a definite locomotory structure. They are non-motile organisms. They can reproduce by both sexual and asexual means.
Examples of sporozoans are Plasmodium.

Note:
These protozoans are unicellular organisms and have heterotrophic modes of nutrition. They are primitive organisms which show many similarities to animals like presence of heterotrophic mode of nutrition, ability to move via locomotory organs.