"Jawed leeches" - termed "Gnathobdellae" or "Gnathobdellida" - are exclusively found among the Hirudiniformes, but the order contains a number of jawless families as well. The jawed, toothed forms make up the aquatic Hirudidae and the terrestrial Haemadipsidae and Xerobdellidae (sometimes included in the preceding but worthy of recognition as an independent family). These might actually form a clade, which would then be placed at superfamily rank,^[1] but it seems that the Hirudidae might rather be close relatives of the carnivorous Haemopidae instead.^[2]

Many of the most well-known leeches belong to this family, most notably the medical leeches, such as the European species, already mentioned, which is prominent among these. Other medical Hirudiniformes of lesser importance are for example other species of the genus Hirudo, the North American medical leech (Macrobdella decora), and the Asian medical leech (Hirudinaria manillensis). Among the better-known bloodsucking land leeches are species belonging to the Asian genus Haemadipsa: they include the Indian leech (H. sylvestris) and the yamabiru or Japanese Mountain Leech (H. zeylanica).