Leech-like thing found in my boot?

I was conducting a field study in a vernal pool in Toledo, OH and water overflowed into my boots. When I was done with the field study, I removed my boots and felt a squirming on my foot. I looked down and saw a grey-black leech-like looking thing on my foot, except it had pincers and was writhing around rather quickly. Any idea on what it might have been?