Difference Between Coelomate and Acoelomate

The key difference between coelomate and acoelomate is that the coelomate is an organism that possesses a true fluid-filled body cavity completely lined by the mesoderm-derived epithelium while the acoelomate is an organism that lacks a body cavity between the digestive tract and outer body wall.

Classification of animals is easy when considering their morphological characteristics. Accordingly, presence and absence of a body cavity, as well as, the type of it have provided the scientists with the major criterion for classification. A body cavity can be plainly defined as a cavity, which lies between the epidermis/body covering and the outer covering of the gastrointestinal cavity. Hence, depending on the type of the body cavity, there are three types of animals namely coelomic, pseudocoelomic and acoelomic. Accordingly, this difference in the type of the body cavity has given rise to many other differences between coelomate and acoelomate even it doesn’t correlate with any evolutionary relationship.

CONTENTS

1. Overview and Key Difference
2. What is Coelomate
3. What is Acoelomate
4. Similarities Between Coelomate and Acoelomate
5. Side by Side Comparison – Coelomate vs Acoelomate in Tabular Form
6. Summary

What is Coelomate?

Coelomates possess a fluid-filled body cavity/true coelom. The mesoderm-derived epithelium outlines the coelom. Therefore, all body organs are suspended within this and have a higher degree of freedom to develop, grow and move independently from the body wall while maintaining more organized structure within the body. Additionally, this type of body cavity protects those delicate, suspended organs by acting as a shock absorber. Also, the fluid-filled coelom acts as a hydrostatic skeleton, which gives support and some sort of a shape, especially to those animals without hard skeletal structures.

Figure 01: Coelomates

Apart from those, coelomic fluid act as a transport medium to many soluble gases and metabolites. Consequently, this is a greater advantage for animals with complex body forms with a low surface to volume ratio. Vertebrates and most of the other animals that have bilateral symmetry posses a true coelom. Hence, they are coelomates.

What is Acoelomate?

Acoelomates as the name implies, lack a fluid-filled body cavity completely lined with the mesoderm. Their body organs are embedded within the mesoderm-derived parenchymal tissues rather than suspended, limiting their freedom to move, develop and grow independently. Lack of a fluid-filled cavity also removes the advantage of the incompressible nature of fluid; thus, making the body organs and the whole body vulnerable to external mechanical pressure.

Figure 02: Acoelomate

Moreover, the lack of a fluid-filled body cavity is one of the major reasons for the rather simple body plan of acoelomic animals. Many acoelomates are dependent on simple diffusion for essential gases and metabolites supply and must have flatter body shapes to increase the surface to volume ratio. Examples for acoelomates are flatworms of the phylum Platyhelminthes.

What are the Similarities Between Coelomate and Acoelomate?

• Both coelomate and acoelomate are triploblastic organisms.
• Also, many of them are invertebrates.

What is the Difference Between Coelomate and Acoelomate?

Coelomate has a true coelom that lined by a mesodermally derived epithelium. On the other hand, acoelomate lacks a fluid-filled body cavity or the true coelom. Therefore, this is the key difference between coelomate and acoelomate. Furthermore, due to the presence of a coelom, internal organs are suspended in the fluid of the coelom, and they are protected unlike in acoelomates. Hence, it is another difference between coelomate and acoelomate.

Moreover, a further difference between coelomate and acoelomate is that the coelomates include both vertebrates and invertebrates while acoelomates include only invertebrates. Also, the coelomate has a complex body form while acoelomate lacks a complex body form. Therefore, it is also a difference between coelomate and acoelomate.

The below infographic presents more detail regarding the difference between coelomate and acoelomate comparatively.

Summary – Coelomate vs Acoelomate

Coelomates and acoelomates are two types of triploblastic organisms that have three germ layers in their embryo. The key difference between coelomate and acoelomate is the presence and absence of a true body cavity or coelom. Coelomate has a fluid-filled body cavity or a true coelom while acoelomate does not have a true coelom. Furthermore, internal organs of the coelomates are protected due to the presence of a coelom while they are not protected in the acoelomates due to the absence of a coelom. Thus, this is the difference between coelomate and acoelomate.

Reference:

1. “Coelom.” Wikipedia, Wikimedia Foundation, 9 Jan. 2019. Available here  
2. “Acoelomates: Definition & Overview.” Study.com. Available here  

Image Courtesy:

1.”Annelid redone w white background”By KDS444 – Own work, (CC BY-SA 3.0) via Commons Wikimedia  
2.”Figure 27 02 05″By CNX OpenStax  (CC BY 4.0) via Commons Wikimedia

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