Commercial pearl is formed by :

Options

A. Oyster
B. Octopus
C. Lamellidens
D. None of these

Answer

To answer the question "Commercial pearl is formed by:", we will analyze the options provided and determine which organism is responsible for the formation of commercial pearls.

### Step-by-Step Solution:

1. **Understanding Commercial Pearls**:
- Commercial pearls, often referred to as nacreous pearls, are primarily produced by certain types of mollusks.

2. **Analyzing the Options**:
- **Option 1: Oyster**:
- Oysters are known to produce pearls. They create pearls as a defense mechanism against irritants, such as parasites or foreign objects. The layers of nacre (mother-of-pearl) are secreted around the irritant, forming a pearl. This option is correct.

- **Option 2: Octopus**:
- Octopuses are soft-bodied, eight-limbed mollusks and do not produce pearls. Therefore, this option is incorrect.

- **Option 3: Lamellidons**:
- Lamellidons belong to the class Bivalvia within the phylum Mollusca, but they are not known for producing commercial pearls. Hence, this option is also incorrect.

- **Option 4: None of these**:
- Since we have already identified that oysters produce commercial pearls, this option is incorrect.

3. **Conclusion**:
- Based on the analysis, the correct answer is **Option 1: Oyster**.

### Final Answer:
Commercial pearl is formed by **Oyster**.