Some 680 species of leech have been described, of which around 100 are marine, 480 freshwater and the remainder terrestrial. The ventral face (right) shows many young leeches. Placobdelloides siamensis, a parasite of turtles in Thailand. In modern times, leeches find medical use in treatment of joint diseases such as epicondylitis and osteoarthritis, extremity vein diseases, and in microsurgery, while hirudin is used as an anticoagulant drug to treat blood-clotting disorders. Leeches have been used in medicine from ancient times until the 19th century to draw blood from patients.
Almost seven hundred species of leech are currently recognised, of which some hundred are marine, ninety terrestrial and the remainder freshwater. In terrestrial species, the cocoon is often concealed under a log, in a crevice or buried in damp soil. The eggs are enclosed in a cocoon, which in aquatic species is usually attached to an underwater surface members of one family, Glossiphoniidae, exhibit parental care, the eggs being brooded by the parent. A minority of leech species are predatory, mostly preying on small invertebrates.
Leach or leech skin#
The jaws used to pierce the skin are replaced in other species by a proboscis which is pushed into the skin. The best-known species, such as the medicinal leech, Hirudo medicinalis, are hematophagous, attaching themselves to a host with a sucker and feeding on blood, having first secreted the peptide hirudin to prevent the blood from clotting. The majority of leeches live in freshwater habitats, while some species can be found in terrestrial or marine environments. The body is muscular and relatively solid, and the coelom, the spacious body cavity found in other annelids, is reduced to small channels. 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. They are closely related to the oligochaetes, which include the earthworm, and like them have soft, muscular segmented bodies that can lengthen and contract. Leeches are segmented parasitic or predatory worms that comprise the subclass Hirudinea within the phylum Annelida.
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