Leeches are invertebrates. They live in shallow ponds and lakes, among plants.
They hook on to creatures like us, and cut a minor hole in our body, and suck our blood. It cannot drain much blood unless you don't notice it for a long time.
They used leeches back in the 1600's, as a remedy to "bad blood."
Leeches are annelids comprising the subclass Hirudinea. There are freshwater, terrestrial, and marine leeches. Like the Oligochaeta, they share the presence of a clitellum. Like earthworms, leeches...