How useful is the study of the nature of body cavity and coelom in the classification of animals?

Explanation

**Step-by-Step Solution:**

1. **Understanding Body Cavity and Coelom:**
- A coelom is defined as a fluid-filled cavity located between the body wall and the gut wall, which is lined by mesoderm on all sides. This structure is crucial for the classification of animals.

2. **Classification Based on Coelom:**
- The presence or absence of a coelom is a significant characteristic in the classification of animals. Animals can be classified into three main categories based on their body cavity:
- **Coelomates:** These animals possess a true coelom, where the body cavity is completely lined by mesoderm. Examples include annelids, mollusks, arthropods, echinoderms, and chordates.
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