In the fist course of evolution, true coelom appeared for the first time in

Options

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

Answer

To solve the question regarding the first appearance of a true coelom in the course of evolution, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Coelom**:
- A coelom is a fluid-filled body cavity that is completely lined by mesoderm. It allows for the development of complex organs and systems.

2. **Identifying the Options**:
- The options provided are:
- A. Annelida
- B. Chordata
- C. Echinodermata
- D. Asteroidea

3. **Arranging the Groups in Evolutionary Order**:
- To find out where the true coelom first appeared, we need to arrange the groups in the order of their evolutionary appearance:
- First: Asteroidea (Echinodermata)
- Second: Annelida
- Third: Chordata

4. **Coelom Development in Each Group**:
- **Asteroidea (Echinodermata)**: They have a coelom, but it is not considered a true coelom in the same sense as in higher organisms.
- **Annelida**: This group is known for having a true coelom. It is the first group in which a true coelom appears.
- **Chordata**: They also possess a true coelom, but they evolved after Annelida.

5. **Conclusion**:
- Based on the evolutionary order and the characteristics of the groups, the first appearance of a true coelom is in **Annelida**.

### Final Answer:
- The answer to the question is **A. Annelida**.

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