The leech and the earthworm both belong to the phylum Annelida. Annelids are segmented worms with a body that is divided into many small, repeating units. They have a closed circulatory system, a digestive system, and a nervous system. The leech and the earthworm are both hermaphrodites, which means they have both male and female reproductive organs. They play an important role in maintaining soil health and are often used as bait for fishing.