florida rock

So I was driving through south florida and on a whim I stopped by a landscaping supply company to see if they had anything I could use. I bought a couple pieces of this "rip rap" material that was pennies a pound. I was thinking of breaking it up and using it as fuge rubble for some extra...

So I removed my torch to treat an infection and found this thing hiding. I had seen it before and thought it was dead but it moves when I shine a light on it. Any ideas what it is?