What is the structure of the circulatory system of annelids and what are its functions?

In annelids, a circulatory system appears for the first time, and a closed one, that is, blood always moves only through the vessels. The function of the circulatory system is to carry oxygen to organs, carry away carbon dioxide, that is, gas exchange.

The circulatory system of worms is represented by vessels. There is no heart. The role of the heart is played by four large vessels that push blood through the body. From these “hearts” the dorsal vessel departs, through which the blood moves to the back of the body of the worm, from there it returns through the abdominal vessel to the “hearts”. From here, the blood moves from front to back again. The abdominal and dorsal vessels themselves are interconnected by transverse vessels (annular).

The blood is red.