acrobdella decora, also known as the North American medicinal leech, is a species of leech found in much of eastern North America in freshwater habitats. M. decora is a parasite of vertebrates, including humans, and an aquatic predator of eggs, larvae, and other invertebrates. It is a medium-sized leech with a spotted greenish-brown back and a reddish or orange underbelly with black spots. It has ten ocelli, or simple eyes, arranged in a horseshoe shape, as well as three long jaws. Internally, a pharynx takes up a tenth of its digestive tract; a stomach, the majority of its body length. The stomach connects to an intestine, followed by a colon, a rectum, and finally an anus located on the leech's back. M. decora, like all leeches, is hermaphroditic, and has twenty testisacs and two ovisacs, in addition to male and female genital pores. First described by Thomas Say in 1824, the species is now placed in the genus Macrobdella. Its closest relative is believed to be the species Macrobdella diplotertia. It is not considered to be endangered. Macrobdella decora is found in North America east of the Rocky Mountains: in southern Canada and the neighbouring parts of the United States. There is, however, one disjunct population of leeches living in northern Mexico. The species may be able to mix and breed randomly across most of its range, but further research into the topic is needed. The saliva of M. decora contains a blood thinner dubbed "decorsin" which may be unique to the species. A comparison of the saliva of M. decora and that of European species has led researchers to the conclusion that blood-sucking in jawed leeches likely evolved fr