Types of Circulatory System
Animals possess two types of circulatory system. They are
1. Open type
2. Closed type
In open type the blood is pumped by heart into blood vessels that open into blood spaces called as sinuses. These sinuses are the body cavities which are called haemocoel. Capillary system is absent. e.g. Arthropods, Molluscs and Ascidias.
In closed type the blood flows in a complete circuit around the body through specific blood vessels. The blood flows from arteries to veins through small blood vessels called capillaries. e.g Vertebrates.