Weird Worm Behavior ?

[qwikcustoms]

Last night after shuting main lights and putting on night led's I noticed a brown worm,looked like a bristle worm near one of my corals. What was weird was that it had a piece of shell substrate and was dragging it to its hole. When I put a light on it it dropped the piece of shell and fled into its hole. This morning when I checked I noticed it moved a ricordia florida and its base that was near it to the entrance of its hole. It moved it about 2-3 inches .I removed the coral and found the worm had moved and wedged a bunch of little substrate pieces around the hole it came from. I was able to get the worm out,I think it might be alive still so I put him in a safe place for now. Any idea what type of worm does this and why,for food ?? shelter??to drive me crazy ?? I know a picture would help alot but cant get one now,sorry,but looking forward to know what it is if anyone can tell me,thanks Paul