Tube -in - tube organization is absent in

Options

A. 1)flatworms
B. 2)roundworms
C. 3)earthworms
D. 4)silkworms

Answer

To solve the question "Tube-in-tube organization is absent in," we will analyze the options provided and determine which organism does not exhibit this body plan.

### Step-by-Step Solution:

1. **Understand Tube-in-Tube Organization**:
- Tube-in-tube organization refers to a body plan where there are two openings: one for the intake of food and the other for the expulsion of waste. This design allows for a more complex digestive system and is associated with a coelom (fluid-filled cavity) between the body wall and the digestive tract.

2. **Identify the Options**:
- The options given are:
- A) Flatworm
- B) Roundworm
- C) Earthworm
- D) Silkworm

3. **Analyze Each Option**:
- **A) Flatworm**:
- Flatworms belong to the phylum Platyhelminthes. They do not have a true coelom and exhibit aacoelomate body plan. Therefore, they lack the tube-in-tube organization.
- **B) Roundworm**:
- Roundworms belong to the phylum Nematoda. They have a pseudocoelom and exhibit tube-in-tube organization, which includes two openings.
- **C) Earthworm**:
- Earthworms belong to the phylum Annelida. They possess a true coelom and exhibit tube-in-tube organization.
- **D) Silkworm**:
- Silkworms belong to the phylum Arthropoda. They also have a true coelom and exhibit tube-in-tube organization.

4. **Conclusion**:
- Based on the analysis, the organism that does not exhibit tube-in-tube organization is the **Flatworm** (Option A).

### Final Answer:
The correct answer is **A) Flatworm**.