Blood flow can be precisely regulated in a closed circulatory system where blood flows inside the blood vessels. Annelids and chordates have a closed circulatory system in which the blood pumped by the heart is always circulated through a closed network of blood vessels.
Open circulatory system is present in arthropods and molluscs (except Cephalopoda) in which blood pumped by the heart passes through large vessels into open spaces or body cavities called sinuses. Mosquito is an arthropod hence it has open circulatory system.