Which of the following statement is incorrect about circulatory system of molluscs?

Options

A. Blood contains a respiratory pigment haemocyanin
B. Non-cephalopod molluscs have open circulatory system
C. Cephalopod molluscs have closed circulatory system
D. Respiratory pigment is haemoglobin dissolved in plasma

Explanation

To determine which statement is incorrect about the circulatory system of molluscs, we can analyze the provided statements one by one:

1. **Statement about Hemocyanin**: The first statement mentions that the blood contains a respiratory pigment called hemocyanin. This statement is correct. In molluscs, hemocyanin, which contains copper, is responsible for oxygen transport, and it gives the blood a blue color.

2. **Statement about Non-Cephalopod Molluscs**: The second statement states that non-cephalopod molluscs have an open circulatory system. This is also correct. Most molluscs, except for cephalopods, possess an open circulatory system where the blood flows freely in open spaces or sinuses.

3. **Statement about Cephalopod Molluscs**: The third statement claims that cephalopod molluscs have a closed circulatory system. This statement is correct as well. Cephalopods, such as octopuses and squids, have a more complex circulatory system that is closed, allowing for more efficient oxygen transport.

4. **Statement about Hemoglobin**: The final statement asserts that the respiratory pigment is hemoglobin dissolved in the plasma. This statement is incorrect. In molluscs, the primary respiratory pigment is hemocyanin, not hemoglobin. Hemoglobin is found in vertebrates and some other organisms, but not in most molluscs.

Based on this analysis, the incorrect statement about the circulatory system of molluscs is:

**Answer**: The respiratory pigment is hemoglobin dissolved in the plasma.