ID please: worm-like creature

[jess128]

I just got 60lbs of fiji in my tank last week and I have no idea how anything on it would survive, but this guy did! I saw it laying between the rocks today while I was cleaning my filter. It's about 6 inches long but I think there was more under the rock. The end of it is pretty thick and it gets thinner as you get closer to the head. When I turned the lights on to get a better look, it started moving underneath the rock. There was what looked like a smaller version (about 2 inches long) near it, just laying on the substrate and was not under a rock. Anyone know what this thing could be? It's kind of creepy...