Respiration of molluscs is by gills called ...........

Answer

**Step-by-Step Solution:**

1. **Identify the Type of Molluscs**: The question specifically refers to the respiration of molluscs. It is important to recognize that there are two main types of molluscs: aquatic and terrestrial.

2. **Aquatic Molluscs**: For aquatic molluscs, respiration occurs through specialized structures known as gills.

3. **Name of the Gills**: The gills in aquatic molluscs are specifically referred to as "ctenidia." Ctenidia are arranged in a comb-like structure, which facilitates the exchange of gases.

4. **Terrestrial Molluscs**: In contrast, terrestrial molluscs do not possess well-developed gills. Instead, they have reduced gills or rely on a cavity for respiration.

5. **Respiratory Cavity in Terrestrial Molluscs**: In terrestrial molluscs, respiration occurs through a cavity known as the "pallial cavity," which functions similarly to lungs.

6. **Conclusion**: Therefore, the answer to the question is that the respiration of aquatic molluscs is by gills called "ctenidia."

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