Animals that have three layers of embryonic tissue but have organs in a cavity that is not completely lined with mesoderm are :

Options

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

Explanation

To solve the question regarding animals that have three layers of embryonic tissue but possess organs in a cavity that is not completely lined with mesoderm, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Embryonic Layers**:
- Animals can be classified based on the number of embryonic tissue layers they possess. The three layers are ectoderm, mesoderm, and endoderm. Animals with these three layers are referred to as triploblastic animals.

2. **Identify the Types of Body Cavities**:
- There are different classifications of animals based on the presence and type of body cavity:
- **Acoelomates**: Animals without a body cavity (e.g., sponges, cnidarians, flatworms).
- **Pseudocoelomates**: Animals with a body cavity that is not completely lined by mesoderm (e.g., roundworms).
- **Coelomates (or Eucelomates)**: Animals with a true coelom, which is a body cavity completely lined by mesoderm (e.g., annelids, echinoderms, chordates).

3. **Analyze the Given Options**:
- **Acoelomate**: This option is incorrect as these animals lack a body cavity.
- **Eucelomate**: This option is also incorrect as these animals have a true coelom, which is fully lined with mesoderm.
- **Pseudocoelomate**: This option is correct because these animals have a body cavity (pseudocoel) that is not completely lined with mesoderm.
- **Stenomate**: This term is not commonly used in this context and is likely incorrect.

4. **Conclusion**:
- Based on the definitions and classifications, the correct answer to the question is **C, Pseudocoelomate**.

### Final Answer:
The animals that have three layers of embryonic tissue but have organs in a cavity that is not completely lined with mesoderm are **C, Pseudocoelomate**.

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