Hirudo is a genus of leeches, commonly known as medicinal leeches. These segmented worms are primarily found in freshwater environments and are known for their ability to attach to hosts and feed on blood. They have been used in traditional medicine for centuries, particularly for their therapeutic properties. The most well-known species within this genus is Hirudo medicinalis, which has been used in modern medicine for bloodletting and promoting healing. The saliva of these leeches contains anticoagulants, which help prevent blood clotting and improve circulation, making them valuable in certain medical treatments.