In molluscs, the respiratory pigment is

Options

A. Haemoglobin
B. Haemocyanin in the blood cells
C. Myoglobin
D. Haemocyanin in the blood plasma

Answer

**Step-by-Step Solution:**

1. **Understanding Mollusca:** Begin by recognizing that Mollusca is a diverse group of invertebrates that includes snails, clams, and squids. They are characterized by their soft bodies, which are often protected by a hard shell.

2. **Identifying Respiratory Pigments:** In many animals, respiratory pigments are crucial for transporting oxygen in the blood. In Mollusca, the common respiratory pigments are hemocyanin and hemoglobin.

3. **Absence of Red Blood Cells:** It is important to note that molluscs do not have red blood cells (RBCs) like vertebrates. Instead, they utilize other substances for oxygen transport.

4. **Hemocyanin as the Main Respiratory Pigment:** The primary respiratory pigment in molluscs is hemocyanin. This pigment contains copper and is responsible for the blue color of the blood in these organisms. Hemocyanin binds to oxygen and is found in the blood plasma of molluscs.

5. **Comparison with Other Pigments:**
- Hemoglobin is typically found in vertebrates and is not the main respiratory pigment in molluscs, although it is present in some specific cases (like the pulmonate snail).
- Myoglobin is found in muscle tissues and is not the primary respiratory pigment in molluscs.

6. **Conclusion:** The correct answer to the question about the respiratory pigment in molluscs is hemocyanin, specifically found in the blood plasma.

**Final Answer:** The respiratory pigment in molluscs is hemocyanin.

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