Higher-level phylogenetic relationships and latest classification of leeches

Leeches in the order Hirudinida comprise approximately 700 species that are distributed worldwide and occupy diverse habitats, including freshwater, marine, and terrestrial habitats. Leeches have traditionally been classified into two main groups, Rhynchobdellida and Arhynchobdellida, on the basis of the presence or absence of a proboscis. However, recent molecular analyses using large datasets have suggested that Rhynchobdellida is a paraphyletic group, and this has led to calls for a new classification that better reflects phylogeny. In addition, recent studies have clarified the previously unresolved phylogenetic relationships among leeches and two leech-like worms, Acanthobdellida and Branchiobdellida. Here, we discuss recent trends in the higher-level phylogenetic relationships and classification of leeches.