Annelids, formerly called annelida, have a closed circulatory system. There are some small annelids that do not have a separate circulatory system, but most annelids have a well-developed closed circulatory system.
Annelids are small segmented worms, such as earthworms, leeches and marine worms. The two main circulatory vessels that can be seen during dissection are the dorsal and ventral blood vessels. These two vessels are the main pumping structures. Blood moves anteriorly in the dorsal vessel and posteriorly in the ventral vessel. In addition to a closed circulatory system, annelids have muscle layers, a digestive tract, a nervous system and an excretory system.