There's a broad estimate of 10-100 million living species on Earth. Where does Hirudio medicinalis fit in to the         grand scheme of things?  Lets first take a look at the leech using the classification system that some people may       recognize from their high school biology class--Linnaean Taxonomy.
  Domain: Eukarya     
         Kingdom: Animalia                                
                 Phylum: Annelidia
                        Class:  Clitellata

                                      Family: Hirudidae
                                            Genus: Hirudo
                                                   Species: Hirudo medicinalis

                                                                                                                                                    Hirudo medicinalis. Photo by Karl Ragnar Gjertsen

The Breakdown


Class relationships of leeches. Rouse and Pleijel (2001).

The tree above shows the class relationships of the annelid phylum, and is based on both morphological characteristics and molecular rDNA. As you can see, the class that Hirudo medicinalis falls under (clitellata) has a question mark by it. There is still some debate as to where the group should be placed in relation to the others.

                                                               Familial relationships of leeches. Investigators-Mark Siddall and Kathleen Apakupakul

This phylogentic tree shows the familial relationship of leeches, and the species within them. Purple represents the
Branchiobdellida and Acanthobdellida, green represents  Glossiphoniidae, blue represents Piscicolidae and Ozobranchidae, red represents Hirudinidae, and pink represents Erpobdellidae. This tree is based on morphological and rDNA relations.



                                            Click here to learn about where Hirudo medicinalis lives