Leeches are bascially segmented worms that live in bodies of water. Leeches suck blood with what are called suckers that are found at each end of the leech. Sucking blood is how they get their nutrition. What is interesting about leeches is how they can sometimes be used to suck blood for medical purposes. The cardiovascular system for leeches is quite intriguing because unlike most animals who have a single heart they have five of them which is extremely interesting.