When my tank crashed a while back I had all my live rock in buckets of water and the temp got down a little low causing a lot of die off on the rock...in the bottom of the bucket you would not imagine the different worms and critters that were dead...several were quite thick, kinda the size of a cheeze string if you know what they are. I wouldn't worry about it in your tank, you probably have many many more just this guy has the guts to poke his head out.