The term aquatic worm refers to any worm-like organism that lives in water environments. There are several synonyms that could be used to describe these organisms. Many aquatic worms are commonly referred to as annelids because they belong to the phylum Annelida, which includes segmented worms. Another term that is often used to describe aquatic worms is oligochaete. This refers specifically to the group of segmented worms that have few setae (hairs) per body segment. Other synonyms for aquatic worms include polychaete, which describes worms that have many setae, and leech, which refers to a specific type of annelid that feeds on the blood of other animals.