Which animal first developed a circulatory system and which one?

The circulatory system first appeared in representatives of annelids. These include the earthworm. These animals have a closed circulatory system, that is, blood moves only through the vessels and does not pour out into the body cavity. Through the abdominal vessel, blood flows to the posterior end of the body, along the dorsal vessel, on the contrary, to the head end. In each of its segments there is an annular vessel, and gas exchange occurs in the capillaries of organs and skin. There is no heart, its role is played by several large annular vessels in the region of the “girdle”.