There are about 9,000 spp. The oligochaetes contain about 6,000 spp. They lack parapodia and setae on their lateral surfaces and all are hermaphroditic. Leeches can be marine, fresh water or terrestrial, but there are only about 500 known species. All are hermaphroditic, they lack parapodia and setae, and all have a small anterior sucker which contains the mouth and a large posterior sucker.
All leeches are ectoparasitic and feed on the blood of either invertebrates or vertebrates.