mollusca has open circulatory system. give reason

Mollusks have an open circulatory system, meaning the blood does not circulate entirely within vessels but is collected from the gills, pumped through the heart, and released directly into spaces in the tissues from which it returns to the gills and then to the heart.

 

Animals that have the open circulatory system are not as vulnerable to pressure as animals that have closed circulatory system. Mollusks can swim and dive to greater depths without the problems that arise with a closed circulatory system. Oxygen and carbon dioxide are served through separate systems. Also the animal has a great ability to control body temperature by  quickly getting rid of the heat.