Question

Blood vascular system of molluscs is
A. Reduced
B. Open
C. Closed
D. Absent

Answer 1

Molluscs pump blood into the hemocoel with the blood diffusing back into the circulatory system between the cells. Blood is transported from the heart into the cavities of the body, where the tissues are surrounded by blood.

Complete answer:
Molluscs constitute the second largest animal phylum. Molluscs are land or marine organisms with an organ-system level of organisation. The body is enclosed by a calcareous shell and has a distinct head, a muscular foot and a visceral hump.

The mollusk circulatory system uses the heart to pump blood throughout the body. All mollusks except those in the Cephalopoda class have an open circulatory system. In an open circulatory system, blood is not stored exclusively in the blood vessels. The heart pumps blood through the blood vessels that run from the gills to the body's cavities called hemocoels. Hemocoel is a blood-filled body cavity that is separate from a fluid-filled coelom. Once the blood is distributed into the blood cells, it is no longer concentrated in the blood vessels and can easily travel to the body’s different tissues in order to provide oxygen and obtain carbon dioxide. The blood then returns to the gills where carbon dioxide is released to the water in the mantle cavity.

Thus, the correct answer is option B i.e., Open.

Note: Cephalopods have developed a closed circulatory system that does not rely on the distribution of blood to tissues in the body. They have a closed circulatory system so that they can move much faster.