Annelids are a group of segmented worms that include familiar creatures like earthworms and leeches. They have soft, elongated bodies divided into segments, which help them move through soil and water. Annelids play important roles in ecosystems, such as improving soil health and breaking down organic matter. These worms have a simple body structure, featuring a coelom, or body cavity, that allows for better movement and organ development. Annelids breathe through their skin and have a closed circulatory system, which means their blood is contained within vessels. This unique anatomy helps them thrive in various environments, from gardens to oceans.