Animals that have three layers of embryonic tissue and have one solid mass of tissue rather than tissues and organs nestled inside a body cavity are :

Options

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

Explanation

To answer the question about animals that have three layers of embryonic tissue and one solid mass of tissue rather than tissues and organs nestled inside a body cavity, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Embryonic Layers**:
- Animals can be classified based on the number of embryonic tissue layers they possess. The three primary layers are ectoderm, mesoderm, and endoderm.

2. **Defining Body Cavities**:
- A body cavity is a fluid-filled space between the body wall and the digestive tract. It allows for the organization of organs and systems.

3. **Identifying Types of Animals**:
- Animals can be categorized into three main groups based on their body cavities:
- **Acoelomates**: These animals do not have a true body cavity. Instead, they have a solid mass of tissue.
- **Coelomates**: These animals possess a true body cavity lined by mesoderm.
- **Pseudocoelomates**: These animals have a body cavity that is not fully lined by mesoderm.

4. **Focusing on Acoelomates**:
- Acoelomates are specifically defined as animals that have three layers of embryonic tissue (ectoderm, mesoderm, and endoderm) and lack a true body cavity. Instead, their organs are embedded within a solid mass of tissue.

5. **Conclusion**:
- Therefore, the answer to the question is that animals with three layers of embryonic tissue and a solid mass of tissue rather than tissues and organs nestled inside a body cavity are called **Acoelomates**.