Leeches are Annelids and there are 3 types of them which are fresh water, terrestrial, and marine leeches. Just like earthworms, leeches are hermaphrodites. Leeches bodies are composed of 34 different segments and in the first six segments off their body they have the suckers which is used to connect to a host to feed on. They also release a type of anesthetic so that the host will not feel the leech on them. The leech uses a combination of mucus and suction to stay attached to the hosts blood stream. As you can probably already tell, leeches feast on animals blood and that is how they get all of their nutrients.
Leeches also reproduce. Begin that leeches are hermaphrodites, leeches reproduce by reciprocal fertilization. The leech grows a sperm sack near the end of the tail and then the leech bites it off, thus reproducing. Leeches also have a clitellum which holds their eggs and secretes the cocoon. Leeches use spermataphores to make the sperm go out. The body figure of a leech is gross as well. Most leeches are extremely slimy and love to stick to mostly everything that contains blood. They dont have feet, just a slimy bottom that helps them move around everywhere.
Leeches have not really evolved a lot over the many years they have been around. Many people think that the leech is in ancestor of the earthworm because it has very similar characteristics but in fact it is in its own kind. I looked everywhere to find where the leech came from but i couldnt really find anything. If i had to guess i would think that the leeches came from some small fresh water fish that is long and slimy.