Background: Medicinal leeches became infamous for their utility in bloodletting popularized in the 19th century, and have seen a recent resurgence in post-operative treatments for flap and replantation surgeries, and in terms of characterization of salivary anticoagulants. Notorious throughout the world, the quintessential leech family Hirudinidae has been taken for granted to be monophyletic, as has the non-bloodfeeding family Haemopidae.
Results: This study is the first to evaluate molecular evidence from hirudinid and haemopid leeches in a manner that encompasses the global scope of their taxonomic distributions. We evaluated the presumed monophyly of the Hirudinidae and assessed previous well-accepted classification schemes. The Hirudinidae were found not to be monophyletic, falling instead into two distinct and unrelated clades. Members of the non-bloodfeeding family Haemopidae were scattered throughout the tree and among traditional hirudinid genera. A combination of nuclear 18S rDNA and 28S rDNA with mitochondrial 12S rDNA and cytochrome c oxidase I were analyzed with Parsimony and with Bayesian methods.
Conclusion: The family Hirudinidae must be refined to include only the clade containing Hirudo medicinalis (European medicinal leech) and related leeches irrespective of bloodfeeding behavior. A second clade containing Macrobdella decora (North American medicinal leech) and its relatives may yet be recognized in Semiscolecidae in order to avoid paraphyly. The African distribution of species from each of the divergent hirudinid clades suggests that a deep divergence took place in the history of the medicinal leeches hundreds of millions of years ago.