What is the Difference Between Protozoa and Metazoa

The main difference between Protozoa and Metazoa is that Protozoa is a group of unicellular primitive animals known as protists whereas Metazoa is a group of multicellular animals. Furthermore, the main forms of protozoans are Amoebae, flagellates, ciliates, and Sporozoa while the two main forms of metazoans are vertebrates and invertebrates.

Protozoa and Metazoa are two forms of eukaryotic animals classified based on their organization of the body.

Key Areas Covered

1. Protozoa
     – Definition, Characteristics, Classification
2. Metazoa
     – Definition, Characteristics, Classification
3. What are the Similarities Between Protozoa and Metazoa
     – Outline of Common Features
4. What is the Difference Between Protozoa and Metazoa
     – Comparison of Key Differences

Key Terms

Animals, Metazoa, Multicellular, Protozoa, Unicellular

Protozoa – Definition, Characteristics, Classification

Protozoa is a group of unicellular eukaryotes belonging to the kingdom Protista. Generally, they are single-celled organisms. As they are eukaryotes, they have a nucleus in their cytoplasm. However, some protozoans have multiple nuclei in their cytoplasm. Also, their cytoplasm consists of two regions known as ectoplasm and endoplasm. Furthermore, some protozoans are free-living in the environment while others are endoparasitic, which means they live inside organisms. Parasitic protozoans can live either inside body tissues or in the blood.

Figure 1: A Protozoan

Furthermore, the main types of protozoans include Amoebae, flagellates, ciliates, and Sporozoa. Mainly, they are classified based on their locomotion. Amoebae use pseudopodia for locomotion. One of the most common parasitic Amoebae in the intestine is Entamoeba histolytica. Also, flagellates or Mastigophora use flagella for their locomotion. On the other hand, ciliates or Ciliophora are the protozoans that use cilia for locomotion. However, Sporozoa are a type of non-motile protozoans.

Metazoa – Definition, Characteristics, Classification

Metazoa is a group of multicellular animals including fish, amphibians, reptiles, birds, and mammals. However, sponges are not considered as metazoans. They are a primitive form of metazoans evolved from choanozoans that are unicellular aquatic protists sometimes forming colonies. Sponges show a single cell-level of organization and do not develop nerves or muscles as found in a regular metazoan. Also, metazoans are monophyletic as they are developed from a single ancestor.

Figure 2: Metazoa

One of the main characteristic features of metazoans is their bilateral body symmetry. Here, animals with a bilateral symmetry belong to a distinct clade known as Bilateria. The two main types of bilaterians are protostomes and deuterostomes. Protostomes include invertebrates such as nematodes, arthropods, and mollusks while deuterostomes include chordates and echinoderms. Furthermore, the other significant features to metazoans are the consumption of organic material, breathing oxygen, ability to move, sexual reproduction, and the development from a hollow sphere of cells known as the blastula during embryonic development.

Similarities Between Protozoa and Metazoa

• Protozoa and Metazoa are two types of eukaryotic organisms.
• They have a nucleus inside their cells.
• Furthermore, they do not have a cell wall as plants and algae.
• Also, they do not undergo photosynthesis.
• Moreover, they use chemical energy stored in nutrients to produce energy for their cellular processes.

Difference Between Protozoa and Metazoa

Definition

Protozoa refers to a group of phyla which comprises the single-celled microscopic organisms, belonging to the kingdom Protista while Metazoa refers to a major division of the animal kingdom that comprises all animals other than protozoans and sponges. Thus, this is the fundamental difference between Protozoa and Metazoa.

Kingdom

Protozoans make up the kingdom Protista while metazoans make up the kingdom Animalia.

Classification

Amoebae, flagellates, ciliates, and Sporozoa are the main forms of protozoans while the two main forms of metazoans are vertebrates and invertebrates.

Cellular Organization

Moreover, their cellular organization is the main difference between Protozoa and Metazoa. Protozoans are unicellular while metazoans are multicellular.

Visibility

In addition, protozoans are microscopic while metazoans can be either microscopic or macroscopic.

Division of Labor

Besides, one other difference between Protozoa and Metazoa is the division of labor. Protozoans have no division of labor while metazoans show the division of labor.

Biological Activities

The single cell of protozoa undergoes all biological activities inside the cytoplasm including digestion, excretion, reproduction, etc. while metazoans have different organ systems and tissues to perform a certain biological activity. Hence, this is another difference between Protozoa and Metazoa.

Type of Reproduction

Furthermore, protozoans undergo both sexual and asexual reproduction while metazoans mainly undergo sexual reproduction.

Sex Differentiation

Also, one other difference between Protozoa and Metazoa is that the protozoans produce identical gametes which cannot be distinguished as male or female while some metazoans are hermaphrodites and others are sexually differentiated.

Evolution

Moreover, protozoans have evolved first while metazoans have evolved from Protozoa. Hence, this is also a difference between Protozoa and Metazoa.

Conclusion

Protozoa is a group of unicellular eukaryotes that are either free-living in the environment or parasitic on plants or animals. They make up the kingdom Protista. In contrast, Metazoa is a group of multicellular animals. The two main types of metazoans are vertebrates and invertebrates. Furthermore, metazoans show higher body organization when compared to Protozoans. Therefore, the main difference between Protozoa and Metazoa is the organization of the body.

References:

1. “About Microbiology – Protozoa.” Microbiology Online, Available Here.
2. “Metazoa.” Science, Available Here.

Image Courtesy:

1. “443598” (CC BY 2.0) via Pxhere
2. “Metazoan Phylogenetic Tree” By Schierwater B, Eitel M, Jakob W, Osigus H-J, Hadrys H, et al. – Figure 2 (CC BY 2.5) via Commons Wikimedia