What is meant by a true coelom? On what basis coelomates are further categorized?

Explanation

### Step-by-Step Solution:

**Step 1: Define True Coelom**
A true coelom is a body cavity that is completely lined by mesodermal epithelial cells. This cavity is formed during embryonic development and is distinct from other types of body cavities, such as a pseudocoelom, which is only partially lined by mesoderm.

**Step 2: Characteristics of True Coelom**
- It is fully enclosed by mesoderm.
- It provides a space for the development and movement of internal organs.
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