Annelids are a phylum of worms characterized by the presence of segmented bodies and bristles called setae on each segment. These features distinguish them from other types of worms, such as flatworms and roundworms, which do not have segmented bodies or setae. Additionally, annelids have a closed circulatory system, meaning that blood is contained within vessels, whereas other worms have an open circulatory system. Annelids also have a digestive system with a mouth and anus, as well as a nervous system consisting of a brain and nerve cords.