Hirudo medicinalis, or the European medicinal leech, is one of several species of leeches used as medicinal leeches.
Hirudo medicinalis
Typical habitat with a large population, Germany
Treating mastitis of a cattle with leech
A caricature of a physician prescribing leeches for a weak, bedbound woman
Leeches are segmented parasitic or predatory worms that comprise the subclass Hirudinea within the phylum Annelida. They are closely related to the oligochaetes, which include the earthworm, and like them have soft, muscular segmented bodies that can lengthen and contract. Both groups are hermaphrodites and have a clitellum, but leeches typically differ from the oligochaetes in having suckers at both ends and in having ring markings that do not correspond with their internal segmentation. The body is muscular and relatively solid, and the coelom, the spacious body cavity found in other annelids, is reduced to small channels.
Image: Sucking leech
Image: Europäischer Platt Egel cropped
Haemadipsa zeylanica, a terrestrial leech
Fossil of a worm that was once considered as leech but denied, from the Waukesha Biota, in the Silurian of Wisconsin