Difference Between Coelomate and Pseudocoelomate

Main Difference – Coelomate vs Pseudocoelomate

Coelomate and pseudocoelomate are two classes of multicellular animals that are classified based on the type of body cavities they have. The body cavity of animals is called the coelom. The coelom develops from the mesoderm during embryonic stages. It surrounds the digestive tract and other organs of the body. The coelom is filled with coelomic fluid that serves as a hydroskeleton. The coelomic fluid allows the free movement of internal organs in the body. It also allows the transport of nutrients, gases, and waste products throughout the body. The main difference between coelomates and pseudocoelomates is that coelomates possess a ‘true’ coelom as their body cavity whereas pseudocoelomates possess a ‘false’ coelom.

Key Areas Covered

1. What is a Coelomate
      – Definition, Characteristics, Examples
2. What is a Pseudocoelomate
      – Definition, Characteristics, Examples
3. What are the Similarities Between Coelomate and Pseudocoelomate
      – Outline of Common Features
4. What is the Difference Between Coelomate and Pseudocoelomate
      – Comparison of Key Differences

Key Terms: Coelomate, Enterocoelomates, Hydroskeleton, Peritoneum, Pseudocoelomate, Schizocoelom, Triploblastic Animals

What is a Coelomate

The term coelomate refers to animals that have fluid-filled body cavities called coeloms located within the mesoderm. Mesoderm is the middle germ layer of triploblastic animals. Therefore, coelom separates the gut from the body wall. All the internal organs are suspended in the fluid called the coelomic fluid. This allows the free internal movement of the organs of the body independently from the body wall. Due to the free internal movements of the organs, the body of coelomates possesses more physiological flexibility compared to animals without a coelom. The coelom also protects the organs from compression and damage. Moreover, coelom also functions as a hydroskeleton and as a circulatory system. The hydroskeleton provides more rigidity to the body. Nutrients, gases, and metabolic wastes are transported through the blood stream in coelomates. The two types of coeloms are schizocoelom and enterocoelom.

Figure 1: Coelomate Structure

The schizocoelom is found in protostomes, whose blastopore develops into the mouth. In schizocoelomates, the body cavity is formed by the splitting of the mesoderm in a process called schizocoely. Their cleavage is spiral, and the fate of each body cell is already determined at its formation. The enterocoelom is found in deuterostomes whose blastopore develops into the anus. In enterocoelomates, the body cavity is formed by outpocketing the primitive gut, which breaks off to form the coelom in a process called enterocoely. The cleavage of the neterocoelomates is radial, and the fate of the cells are not determined at their formation. Therefore, these cells can differentiate into many cell types. The basic structure of a coelomate animal is shown in figure 1. 

What is a Pseudocoelomate

The term pseudocoelomate refers to triploblastic invertebrates with a fluid-filled body cavity between endoderm and the mesoderm. The endoderm is the innermost germ layer in triploblastic animals. The pseudocoelom is the space in the blastula, which is also called the blastocoel. Pseudocoelom acts as the medium for the circulation of nutrients, gases, and waste products since pseudocoelomates lack a closed circulatory system. Moreover, the psuedocoelom serves as a hydroskeleton, which provides structural support.

Figure 2: Pseudocoelomate Structure

Nematoda, Entoprocta, Rotifera, Acenthocephala, and Gastrotrica are the examples of pseoducoelomates. The basic structure of a pseudocoelomate is shown in figure 2. 

Similarities Between Coelomate and Pseudocoelomate

• Coelomate and pseudocoelomate contain fluid-filled body cavities.
• Both coelomates and pseudocoelomates are triploblastic animals that possess three germ layers called endoderm, mesoderm, and ectoderm.
• Both coelomates and pseudocoelomates possess complete digestive tracts.
• The body cavity of both coelomates and pseudocoelomates serves as a hydroskeleton.
• Both coelomates and pseudocoelomates possess a peritoneum.

Difference Between Coelomate and Pseudocoelomate

Definition

Coelomate: A coelomate is an organism with a body cavity between the body wall and the digestive tract.

Pseudocoelomate: A pseudocoelomate is an invertebrate with a fluid-filled body cavity between the endoderm and the mesoderm.

Alternative Names

Coelomate: Coelomates are called eucoelomates.

Pseudocoelomate: Pseudocoelomates are called blastocoelomates and hemocoelomates.

Body Cavity

Coelomate: Coelomates possess a body cavity called coelom.

Pseudocoelomate: Pseudocoelomates possess a body cavity called pseudocoelom.

Location of the Body Cavity

Coelomate: The body cavity of coelomates is inside the mesoderm.

Pseudocoelomate: The body cavity of pseudocoelomates is between endoderm and mesoderm.

Peritoneum

Coelomate: The body cavity of coelomates is lined with peritoneum.

Pseudocoelomate: The body cavity of pseudocoelomates is partially lined with peritoneum.

Origin of the Body Cavity 

Coelomate: The coelom is derived by splitting of the mesoderm.

Pseudocoelomate: The pseudocoelom is derived from the blastocoel of the embryo.

Nutrients 

Coelomate: In the coelom, the nutrients circulate through the blood stream.

Pseudocoelomate: In the pseudocoelom, the nutrients diffuse through diffusion and osmosis.

Organization of the Organs

Coelomate: The organs of the coelomates are well-organized inside the coelom.

Pseudocoelomate: The organs of the pseudocoelomates are less-organized inside the pseudocoelom.

Vertebrates/Invertebrates

Coelomate: Coelomates can be either vertebrates or invertebrates.

Pseudocoelomate: Pseudocoelomates are invertebrtaes.

Examples

Coelomate: Annelida, Arthropoda, Mollusca, Echinordermata, Hemichordata, and Chordate are coelomates.

Pseudocoelomate: Nematoda, Entoprocta, Rotifera, Acenthocephala, and Gastrotrica are examples of pseoducoelomates.

Conclusion

Coelomate and pseudocoelomate are two types of animals classified based on the type of body cavity present in each animal. Both coelomates and pseudocoelomates are triploblastic animals with complete digestive systems. Coelomates possess a body cavity called coelom inside the mesoderm. Pseudocoelomates possess a body cavity called pseudocoelom between the endoderm and the mesoderm. Both coelom and pseudocoelom are fluid-filled cavities, which serve as hydroskeletons. The main difference between coelomate and pseudocoelomate is the type of body cavity in each class of animals. 

Reference:

1. Anissimov, Michael, and Bronwyn Harris. “What is a Coelom?” WiseGEEK, Conjecture Corporation, 12 Aug. 2017, Available here, Accessed 6 Sept. 2017.
2. “Pseudocoelomate.” Infoplease, Available here. Accessed 6 Sept. 2017.

Image Courtesy:

1. “Coelomate 01” By Philcha (talk) – Own work (Public Domain) via Commons Wikimedia