Body cavity is the cavity present between body wall and gut wall. In some animals the body cavity is not lined by mesoderm. Such animals are called

Options

A. acoelomate
B. pseudocoelomate
C. coelomate
D. haemocoelomate

Answer

To solve the question regarding the classification of animals based on the presence and lining of body cavities, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Body Cavity**:
- The body cavity is defined as the space between the body wall and the gut wall in animals. It plays a crucial role in the organization of the internal structures.

2. **Types of Body Cavities**:
- There are different classifications of animals based on the presence and type of body cavity:
- **Acoelomates**: Animals that do not have a body cavity at all.
- **Coelomates**: Animals that have a true coelom, which is a body cavity lined by mesoderm.
- **Pseudocoelomates**: Animals that have a body cavity not entirely lined by mesoderm; instead, the cavity is partially lined.
- **Hemocoelomates**: Animals that possess a hemocoel, which is a blood-filled body cavity.

3. **Identifying the Correct Term**:
- The question specifically asks for animals whose body cavity is not lined by mesoderm. This definition matches with **pseudocoelomates**.

4. **Conclusion**:
- Therefore, the correct answer to the question is **Pseudocoelomates** (Option B).

### Final Answer:
**Pseudocoelomates** are the animals in which the body cavity is not lined by mesoderm.

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