Body cavity is lined by mesoderm in

Options

A. Aschelminthes
B. Annelida
C. Platyhelminthes
D. Ctenophora

Answer

To solve the question "Body cavity is lined by mesoderm in," we will analyze the given options step by step.

### Step 1: Understand the Types of Body Cavities
- There are different types of body cavities in animals:
- **Acoelomate**: No body cavity (e.g., flatworms).
- **Pseudocoelomate**: Body cavity not completely lined by mesoderm (e.g., roundworms).
- **Coelomate**: Body cavity completely lined by mesoderm (e.g., annelids, mollusks, and vertebrates).

### Step 2: Analyze Each Option
1. **Acoelomates**: These animals do not have a body cavity lined by mesoderm. Therefore, this option is incorrect.

2. **Annelida**: This group includes segmented worms like earthworms. They possess a true coelom, which is a body cavity lined by mesoderm. This option is a strong candidate for the correct answer.

3. **Lophotrochozoa**: This is a broader category that includes several phyla, but not all members have a body cavity lined by mesoderm. Thus, this option is not specific enough to confirm the presence of a mesoderm-lined cavity.

4. **Cnidaria**: This group includes jellyfish and corals. They have a simple body structure and do not possess a true coelom. Therefore, this option is also incorrect.

### Step 3: Conclusion
After analyzing all the options, the only group that has a body cavity lined by mesoderm is **Annelida**. Thus, the correct answer is:

**Answer: Annelida**

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