Question

Which among the following has an open circulatory system?

• A. Arthropoda
• B. Mollusca
• C. Annelida
• D. Coelenterata

Answer 1

Answer: (A), (B)

Mollusca

The correct options are A and B.

Explanation of correct option:

1. It is a type of circulatory system.
2. In an open circulatory system, the heart pumps blood through large veins into open cavities in the body known as sinuses.
3. There is no genuine heart or blood arteries in this arrangement.
4. These species blood is a mixture of blood and haemolymph, an interstitial fluid.
5. Molluscs and arthropods both have an open circulatory system.

Explanation of incorrect options:

Option C:

1. Annelids have a close circulatory system.
2. Blood is circulated through blood vessels, capillaries, and the heart.
3. Blood glands are present on the 4th, 5th, and 6th segments and produce blood cells and haemoglobin which is dissolved in plasma.
4. Example: earthworm.

Option D:

1. The circulatory system of coelenterates is absent.
2. Circulation occurs by diffusion across the tissue layer.
3. All cells are in direct contact with one another, allowing for exchange.
4. Example: comb jellies.

Final answer: Arthropoda and Mollusca have an open circulatory system.