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

Explanation

To solve the question regarding animals with a body cavity that is not lined by mesoderm, 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.

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 (e.g., flatworms).
- **Coelomates**: Animals that have a true coelom, which is a body cavity completely lined by mesoderm (e.g., annelids, mollusks, arthropods).
- **Pseudocoelomates**: Animals that have a body cavity that is not completely lined by mesoderm. Instead, the cavity is present in the form of scattered pouches between the ectoderm and endoderm.

3. **Identifying Pseudocoelomates**: The term "pseudocoelomate" comes from "pseudo," meaning false, and "coelom," meaning cavity. This indicates that while there is a cavity, it is not a true coelom because it lacks a complete mesodermal lining.

4. **Examples of Pseudocoelomates**: A common example of pseudocoelomates is roundworms (phylum Nematoda). These organisms have a body cavity that is not lined by mesoderm.

5. **Conclusion**: Therefore, the animals that have a body cavity not lined by mesoderm are referred to as **pseudocoelomates**.

### Final Answer:
The animals with a body cavity that is not lined by mesoderm are called **Pseudocoelomates**.

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