Which among the following have an open circulatory system?

i. Arthropoda

ii. Mollusca

iii. Annelida

iv. Coelenterata

The open circulatory system is a type of circulatory system in which blood is pumped by the heart directly into the body cavities, where tissues are surrounded by the blood and not into blood vessels.

Example of animal groups having an open circulatory system are arthropods and mollusks.