True enterocoelic coelom appeared first during the course of evolution in :-

Options

A. Echinodermata
B. Annelida
C. Chordata
D. Protozoa

Answer

To solve the question regarding which group first exhibited a true enterocoelic coelom during the course of evolution, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Coelom**:
- A coelom is a fluid-filled body cavity that is completely lined by mesoderm. There are different types of coeloms, including acoelomate (no coelom), pseudocoelomate (a body cavity not completely lined by mesoderm), and coelomate (true coelom).

2. **Identify the Types of Coelom**:
- True enterocoelic coelom is formed from pouches that pinch off from the digestive tract during embryonic development.

3. **Evaluate the Options**:
- **Option 1: Echinodermata**:
- Echinoderms have a coelom but it is not a true enterocoelic coelom; they possess a hemocoel.
- **Option 2: Annelida**:
- Annelids are known to have a true coelom that is enterocoelic in nature. This is the correct option.
- **Option 3: Chordata**:
- Chordates also possess a true coelom, but they evolved later than annelids.
- **Option 4: Protozoa**:
- Protozoans are acoelomate, meaning they do not have a coelom at all.

4. **Conclude the Correct Answer**:
- Based on the evaluation, the first appearance of a true enterocoelic coelom in evolution is found in **Annelida** (Option 2).

### Final Answer:
The true enterocoelic coelom appeared first during the course of evolution in **Annelida**.

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