Annelida. While some small segmented worms of the phylum Annelida have no separate circulatory system, most have a well-developed closed system.

What type of circulatory system do annelids have?

Unlike most mollusks, annelids have a closed circulatory system. In a closed circulatory system, blood is always contained within blood vessels.

Does an earthworm have a closed or open circulatory system?

Most vertebrates and some invertebrates, like this annelid earthworm, have a closed circulatory system. In (b) open circulatory systems, a fluid called hemolymph is pumped through a blood vessel that empties into the body cavity.