Introduction:
The nature of the body cavity, called the coelom, is an important criterion used in the classification of animals. It helps in understanding the structural organisation and evolutionary relationships among different animal groups.
What is a coelom?
Coelom is a fluid-filled cavity present between the body wall and the alimentary canal. It is lined by mesoderm and accommodates internal organs.
Types of body cavity and their importance in classification:
1. Acoelomates
Animals in which the body cavity is absent are called acoelomates. The space between the body wall and gut is filled with solid tissue.
Example: Platyhelminthes (flatworms)
This condition indicates a lower level of body organisation.
2. Pseudocoelomates
Animals having a body cavity that is not completely lined by mesoderm are called pseudocoelomates. This cavity is derived from the blastocoel.
Example: Aschelminthes (roundworms)
This represents an intermediate level of organisation.
3. Coelomates
Animals possessing a true coelom completely lined by mesoderm are called coelomates.
Example: Annelida, Arthropoda, Mollusca, Echinodermata, Chordata
A true coelom allows better organ development, movement and physiological functions.
Importance of coelom in classification:
• Helps in grouping animals based on internal organisation
• Reflects the level of complexity and evolutionary advancement
• Assists in understanding functional specialisation of organs
• Provides a reliable basis for distinguishing major animal phyla
Conclusion:
Thus, the study of the nature of body cavity and coelom is highly useful in animal classification as it reveals structural complexity and evolutionary relationships, making classification more natural and scientific.
| List - I | List – II | ||
| A. | Chondrichthyes | i. | Clarias |
| B. | Cyclostomata | ii. | Carcharodon |
| C. | Osteichthyes | iii. | Myxine |
| D. | Amphibia | iv. | Ichthyophis |