Leeches
Leeches are segmented worms that reside mostly in freshwater environments and are widespread. Leeches feed on the blood of vertebrates and invertebrates. For centuries, leeches were used for medicinal purposes in order to drain blood from humans in belief that this got rid of the disease or condition that the individual was infected with. Like the earthworm, the leech breathes through its skin by absorbing oxygen and exerting carbon dioxide and other waste products.