Question

Which among the following have an open circulatory system?

(i) Arthropoda
(ii) Mollusca
(iii) Annelida
(iv) Coelenterata

• A. (i) and (ii)
• B. (iii) and (iv)
• C. (i) and (iii)
• D. (ii) and (iv)

Answer 1

Answer: (A)

(i) and (ii)

The open circulatory system is a type of circulatory system which is common to molluscs and arthropods. Open circulatory systems (evolved in crustaceans, insects, mollusks and other invertebrates) pump blood into a hemocoel with the blood diffusing back to the circulatory system between cells. Blood is pumped by a heart into the body cavities, where tissues are surrounded by the blood.

Vertebrates and a few invertebrates have a closed circulatory system. In the closed circulatory systems, the blood is closed at all times within vessels of different sizes and wall thicknesses. In this type of system, blood is pumped by a heart through vessels and does not normally fill body cavities.