Annelids are a diverse group of segmented worms that include familiar species such as earthworms and leeches. They are characterized by their long, cylindrical bodies divided into segments, which allow for greater flexibility and movement in their environments. These creatures play vital roles in ecosystems, particularly in soil health and nutrient cycling. Annelids can be found in various habitats, from marine environments to freshwater and terrestrial ecosystems, showcasing their adaptability and ecological importance.