Phylum : Annelida
Class : Hirudinea
Genus : Hirudiniaria

Leeches are segmented worms that belong to the phylum Annelida and comprise the subclass Hirudinea. Like other oligochaetes, such as earthworms, leeches share a clitellum and are hermaphrodites.

Nevertheless, they differ from other oligochaetes in significant ways. For example, leeches do not have bristles and the external segmentation of their bodies does not correspond with the internal segmentation of their organs. Their bodies are much more solid as the spaces in their coelom are dense with connective tissues. They also have two suckers, one at each end.

The majority of leeches live in freshwater environments, while some species can be found in terrestrial and marine environments, as well. Most leeches are hematophagous, as they are predominantly blood suckers that feed on blood from vertebrate and invertebrate animals. Almost 700 species of leeches are currently recognized, of which some 100 are marine, 90 terrestrial and the remainder freshwater.

Leeches, such as the Hirudo medicinalis, have been historically used in medicine to remove blood from patients. The practice of leeching can be traced to ancient India and Greece, and continued well into the 18th and 19th centuries in both Europe and North America. In modern times, the practice of leeching is much rarer and has been replaced by other contemporary uses of leeches, such as the reattachment of body parts and reconstructive and plastic surgeries and, in Germany, treating osteoarthritis.

Some facts about Leeches

a) 700 Known leech species
b) Only 5 are used for medicinal purpose
c) It has 32 brains
d) Leeches die after one or to bouts of reproduction
e) 3 sets of jaw
f) Each jaw has around 100 teeth
g) 4 to 10 hour bleeding +nt after leech application
h) Leeches can live up to one year without food so you don't need to feed them
i) Life span of leech - 10yr