In a closed circulatory system, blood is pumped into sinuses instead of vessels
An open circulatory system allows direct diffusion of nutrients and gases to tissues
A closed circulatory system is only found in invertebrates
Only vertebrates have an open circulatory system
In an open circulatory system (e.g., Arthropods), blood is pumped into open spaces (hemocoel),
facilitating direct diffusion of gases and nutrients. In a closed system (e.g., Annelids, Chordates),
blood circulates within vessels.