European medicinal leech

The European medicinal leech, a species of annelid, was historically used to treat various human ailments. Today, it is a source of anticoagulants, particularly after surgical procedures.123

Annelids are a phylum of invertebrate animals characterized by segmented bodies and a coelom, or body cavity. While most annelids have bristles called setae, leeches (subclass Hirudinea) have reduced coeloms and lack setae. Leeches typically have a mouth sucker at the front and a larger sucker at the rear, with all species possessing 34 body segments. They breathe through their skin and have a digestive system capable of storing food for extended periods. Leeches are hermaphroditic, meaning they have both male and female reproductive organs, but require cross-fertilization. Their saliva contains substances that numb the wound, dilate blood vessels, and prevent clotting, with the anticoagulant hirudin being a key component.43