Hirudo medicinalis, commonly known as the medicinal leech, is a species of leech used for medicinal purposes. However, there are several other terms that can be used as synonyms for this organism. These include the medicinal water leech, the European medicinal leech, and the medicinal worm. This leech is known for its ability to produce a natural anticoagulant, hirudin, which is used in therapeutic procedures to prevent blood clots. Medicinal leeches have been used since ancient times and are still used today in modern medicine for various treatments. Hirudo medicinalis can be found in freshwater habitats throughout Europe, Asia, and North Africa.