sure is flat worms..I got a Melanarus Wrasse and it demolished them!.. I was told by Ali at Amazing Aquarium and Reefs that 9/10 times they eat up the flat worms, so i bought one on the spot and within a week all the hundreds of flat worms chilling on the glass vanished... but so did some of my shrimps :-/... tradeoff was worth it..
its been months since and the flat worms that had encrusted the rocks, frags, and glass has almost vanished..