Just an update. I did some more research and found that these will eat some LPS corals. They actually absorb the stinging cells from the corals into their bodys and use them as self defense. I also noticed that they were eating my torch and my hammer coral. I could tell they were eating them...
I found these in my tank recently and I am wondering if they are bad news. They are not your common red flatworm (I have those too). They are about 1.5 inches long (or 4-5cm), white on the bottom, and sandy brown on top. I know there are at least three. They like to hide on my branching...