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
(a) Acoelomate
(b) Pseudocoelomate
(c) Coelomate
(d) Haemocoelomate

Options

A. Acoelomate
B. Pseudocoelomate
C. Coelomate
D. Haemocoelomate

Answer

To solve the question regarding the classification of animals based on their body cavity, 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. It plays a crucial role in the organization of an animal's body structure.

2. **Types of Body Cavities**: There are different classifications of animals based on the presence and type of body cavity:
- **Acoelomate**: Animals that do not have a body cavity. Their body is solid without any cavity between the body wall and gut wall.
- **Pseudocoelomate**: Animals that have a body cavity that is not lined by mesoderm. This cavity is derived from the blastocoel and is present between the endoderm (gut) and mesoderm.
- **Coelomate (or Eucelomate)**: Animals that possess a true coelom, which is a body cavity completely lined by mesoderm.
- **Haemocoelomate**: Animals that have a hemocoel, which is a blood-filled cavity, but this term is less commonly used in the context of body cavity classification.

3. **Identifying the Correct Answer**: The question specifies that the body cavity in some animals is not lined by mesoderm. This description matches the definition of **Pseudocoelomate** animals, as they have a body cavity that is not lined by mesoderm.

4. **Final Answer**: Based on the definitions and classifications, the correct answer to the question is **(b) Pseudocoelomate**.