Helobdella is a genus of leeches in the family Glossiphoniidae, the freshwater jawless leeches. They occur worldwide.These are small, flat leeches which do not feed on blood.Several species in this genus are used as model organisms in the study of developmental biology.It has been difficult to define species in this genus without DNA analysis. Like other leeches in this family, some Helobdella species are polymorphic, coming in different colors and patterns.