Find out the correct option regarding following organisms, Fasciola, Ascaris, Nereis, Periplaneta :-

Options

A. Except Fasciola, rest all have a complete digestive system
B. Ascaris and Nereis have internal fertilisation
C. Except Ascaris all others show metamerism
D. Periplaneta has compound eyes rest others have simple eyes

Answer

To solve the question regarding the organisms Fasciola, Ascaris, Nereis, and Periplaneta, we will analyze each organism based on the options provided.

### Step-by-Step Solution:

1. **Identify the Organisms:**
- **Fasciola**: A genus of parasitic flatworms, commonly known as liver flukes.
- **Ascaris**: A genus of parasitic roundworms, commonly known as intestinal roundworms.
- **Nereis**: A genus of polychaete worms, commonly known as ragworms.
- **Periplaneta**: A genus that includes the American cockroach.

2. **Analyze the Digestive Systems:**
- **Fasciola**: It has an incomplete digestive system. It has a mouth, pharynx, esophagus, and intestine, but does not have an anus.
- **Ascaris**: It has a complete digestive system with a mouth and anus.
- **Nereis**: It also has a complete digestive system.
- **Periplaneta**: It has a complete digestive system.

**Conclusion**: Except for Fasciola, all the other organisms (Ascaris, Nereis, and Periplaneta) have a complete digestive system.

3. **Evaluate Fertilization Methods:**
- **Ascaris**: Internal fertilization occurs in Ascaris.
- **Nereis**: External fertilization occurs in Nereis.

**Conclusion**: The statement that Ascaris and Nereis have internal fertilization is incorrect.

4. **Examine Metamerism:**
- **Fasciola**: Not metameric.
- **Ascaris**: Not metameric.
- **Nereis**: Exhibits metamerism (segmentation).
- **Periplaneta**: Exhibits metamerism (segmentation).

**Conclusion**: The statement that except for Ascaris, all other organisms show metamerism is incorrect.

5. **Check Eye Types:**
- **Fasciola**: Lacks eyes.
- **Ascaris**: Lacks eyes.
- **Nereis**: Possesses simple eyes.
- **Periplaneta**: Has compound eyes.

**Conclusion**: The statement that Periplaneta has compound eyes while the others have simple eyes is incorrect.

### Final Answer:
The correct option regarding the organisms is that **except Fasciola, the rest all have a complete digestive system**.