A phylogenetic revision of the medicinal leeches of the world (Hirudinidae, Macrobdellidae, Praobdellidae)

The term "medicinal leech" refers to more species than just Hirudo medicinalis, the preferred species for bloodletting in 19 th century Europe. In the past, freshwater, leeches with similar morphological characteristics to H. medicinalis have been divided into two families: the bloodfeeding Hirudinidae and the non-bloodfeeding Haemopidae. With a broader taxon sampling than in previous analyses, an analysis of multiple nuclear (18S rDNA and 28S rDNA) and mitochondrial (12S rDNA and cytochrome c oxidase I) gene fragments found Hirudinidae not to be monophyletic, instead placing in two independently originated lineages separated by the two families of terrestrial leeches, Haemadipsidae and Xerobdellidae. Members of Haemopidae were scattered among members of Hirudinidae of both lineages, thus rendering Haemopidae polyphyletic. The lineage containing H. medicinalis retained the name Hirudinidae, while the other lineage was shown to consist of three families: Macrobdellidae (North and South American bloodfeeders), Semiscolecidae (South American non-bloodfeeders), and Praobdellidae (a biogeographically diverse clade of species that feed primarily from mammalian mucous membranes). With the familial relationships within these two lineages established, attention was given to revising the intra-familial and generic relationships. Two new genera and two new species resulted from these investigations: Tyrannobdella rex n. gen. n. sp., a leech found feeding inside the nasal passages of humans placed within Praobdellidae, Mesobdella lineata was re-described as Parapraobdella lineata n. gen. within Praobdellidae, and Hirudinaria bpling n. sp. placed within the Hirudinidae. Endosymbiotic bacteria from the digestive tracts of members of the Hirudinidae, Macrobdellidae, and Praobdellidae were detected and determined to be Aeromonas species as well as an unculturable Bacteroidetes. The Aeromonas isolates did not show a predictable association based on the phylogeny of the leech hosts or geography, while the Bacteroidetes isolates did show a correlation with leech taxonomy. An analysis with the most thorough taxon sampling to date of the families of Hirudiniformes and Erpobdelliformes was performed. Gastrostomobdellidae, a group of macrophagous leeches hypothesized to be similar to Erpobdelliformes or Hirudiniformes, was strongly supported within Erpobdelliformes. The establishment of the relationships provides a basis for further systematic study, as well as a investigations into the evolution of these charismatic worms.