Nacre or mother of pearl is secreted by mantle's

Options

A. Cubical epithelial cells
B. Columnar epithelial cells
C. Columnar endothelial cells
D. Cubical endothelial cells.

Answer

### Step-by-Step Solution:

1. **Understanding Nacre (Mother of Pearl)**:
- Nacre, also known as mother of pearl, is a composite material found in mollusks. It is composed of both organic and inorganic compounds.

2. **Location of Nacre**:
- Nacre is present as the inner layer of the shell in mollusks. This layer is crucial for the protection of the mollusk's soft body.

3. **Secretion of Nacre**:
- The secretion of nacre is performed by specific cells located in the mantle of the mollusk. The mantle is a significant part of the mollusk's anatomy that plays a role in shell formation.

4. **Identifying the Correct Cell Type**:
- The cells responsible for secreting nacre are known as columnar epithelial cells. These cells line the inner cavity of the mantle and are specialized for secretion.

5. **Characteristics of Nacre**:
- Nacre is known for its hard, shiny, and resilient properties. It not only forms the inner layer of the shell but also contributes to the outer coating of pearls.

6. **Conclusion**:
- Based on the above information, the correct answer to the question is that nacre or mother of pearl is secreted by **columnar epithelial cells**.

### Final Answer:
**B. Columnar epithelial cells**

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