The Medicinal Leech (Hirudo verbenaand Hirudo medicinalis) is an invertebrate parasitic worm, and an annelid. It is related to the earthworm. It is called medicinal because doctors have used the leech to draw blood from patients.
There are two types of true leeches: Rhynchobdellida (with a proboscis to puncture the skin of animals) and Arhynchobdellida (without a proboscis). The Medicinal Leech (Hirudo verbena) is a Arhynchobdellida Hirudiniformes (a leech without a proboscis, but with jaws at the front of the mouth).
The Medicinal Leech has a flat, soft, muscular, segmented body without a backbone or skeleton. Therefore, it is an invertebrate. Its upper part is grey with pinkish stripes, or mottled grey-pink-brown, and its underbelly is pale-grey. Its body can lengthen and contract (i.e. get bigger and smaller) as it moves. It has suckers on it mouth and its tail end (anterior and posterior suckers).