What is the Difference Between Metazoa and Eumetazoa

The main difference between Metazoa and Eumetazoa is that Metazoa is a group of multicellular animals excluding Porifera (sponges) whereas Eumetazoa is a group of multicellular animals excluding Porifera and Placozoa. Here, Porifera and Placozoa are classified in a separate subkingdom known as Parazoa. 

Metazoa and Eumetazoa are two taxonomic groups of multicellular animals. Furthermore, the tissues of metazoans may be or may not be organized into true tissues while the tissues of eumetazoans are organized into true tissues.

Key Areas Covered

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

Key Terms

Eumetazoa, Metazoa, Multicellular Animals, Placozoans, Sponges

Metazoa – Definition, Characteristics, Classification

Metazoa is a group of organisms comprising of multicellular animals excluding sponges. Sponges are a primitive form of metazoans. They have evolved from choanozoans that are unicellular aquatic protists, sometimes forming colonies. Moreover, sponges show a single cell-level of organization; hence, there is no formation of tissues in their body. However, the cells of the body of metazoans form tissues. Most of them have tissues organized into true tissues. Nevertheless, placozoans, the most primitive invertebrates, have a body made up of thousands of cells of four types. That means; they do not have tissues organized into true tissues.

Figure 1: Trichoplax adhaerens – A Placozoan

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.

Eumetazoa – Definition, Characteristics, Classification

Eumetazoa is a group of multicellular animals excluding both sponges and placozoans. The main characteristic feature of eumetazoans is the presence of organized tissues into true tissues. Therefore, they have tissues developed into nerves or muscles. Further, these tissues of eumetazoans have three germ layers. Moreover, their embryo goes through the gastrula stage during embryonic development.

Figure 2: Eumetazoans

Furthermore, the two subgroups of eumetazoans are Radiata and Bilateria. The clade Radiata includes both echinoderms and ctenophores, and they have radial body symmetry. On the other hand, the clade Bilateria processes bilateral body symmetry. The two main types of bilaterians are protostomes and deuterostomes. Protostomes include invertebrates such as nematodes, arthropods, and mollusks while deuterostomes include chordates including vertebrates.

Similarities Between Metazoa and Eumetazoa

• Metazoa and Eumetazoa are two taxonomic groups of multicellular animals.
• They are monophyletic as they are developed from a single ancestor.
• Also, they include all vertebrates and most invertebrates.
• However, both groups exclude sponges.
• Moreover, they have tissues and bilateral or radial body symmetry.
• Furthermore, consumption of organic material, breathing oxygen, ability to move, sexual reproduction, and the growth from a hollow sphere of cells known as blastula during embryonic development are their other main characteristic features.

Difference Between Metazoa and Eumetazoa

Definition

Metazoa refers to a major division of the animal kingdom that comprises all animals other than protozoans and sponges while Eumaazoa refers to a group of multicellular animals excluding the Porifera (sponges) and Placozoa. Thus, this is the main difference between Metazoa and Eumetazoa.

Type of Animals

Metazoa includes all eumetazoans and placozoans while Eumetozoa includes all vertebrates and invertebrates excluding placozoans. Hence, this is another difference between Metazoa and Eumetazoa.

Tissue Organization

Moreover, the tissues of metazoans may or may not be organized into true tissues while the tissues of eumetazoans are organized into true tissues.

Characteristic Features

Furthermore, an important difference between Metazoa and Eumetazoa is their characteristic features. The characteristic features of metazoans are the consumption of organic material, breathing oxygen, ability to move, sexual reproduction, and growth from a hollow sphere of cells known as blastula during embryonic development while the characteristic features of eumetazoans are the presence of true tissues, neurons, and an embryo that goes through a gastrula stage.

Conclusion

Metazoa is a group of multicellular animals excluding sponges. On the other hand, Eumetazoa is a somewhat small group of multicellular animals excluding both sponges and placozoans. Moreover, the body of metazoans contain tissues which may be or may not be organized into true tissues while the body of eumetazoans contains tissues organized into true tissues. Therefore, the main difference between Metazoa and Eumetazoa is the tissue organization in the body.

References:

1. “Metazoa.” Science, Available Here.
2. Woodward, Denise. “Animals I – An Overview of Phylogeny and Diversity and the Parazoa, Radiata, Acoelomates and Psuedocoelomates” Biology 110 – Basic Concepts and Biodiversity, Atlassian Confluence, 30 Sept. 2013, Available Here.

Image Courtesy:

1. “Trichoplax adhaerens photograph” By Bernd Schierwater – Eitel M, Osigus H-J, DeSalle R, Schierwater B (2013) Global Diversity of the Placozoa. PLoS ONE 8(4): e57131. doi:10.1371/journal.pone.0057131 (CC BY 4.0) via Commons Wikimedia   
2. “Animalia diversity” By User:Stemonitis – Compiled from other Commons images: File:Loligo vulgaris.jpg, File:Jelly Monterey.jpg, File:Panthera tigris cropped.jpg, File:Aphthona flava flea beetle.jpg and File:Eunereis longissima.jpg (CC BY-SA 2.5) via Commons Wikimedia