OMG a monster in my tank!

[Borderjumper]

Ive had this tank up for years. Nothing much surprises me anymore, but this morning when the lights can on there was a big brown patch of I thought sponge on the side of a rack I keep my acan frags in.. after a cup of coffee I realized that a sponge couldnt have grown overnight.. so I went and poked it ( I poke things alot when I dont know what they are) and it frickin moved!

Its a flat worm or something, but its an inch wide and like 3-4 inches long depending on how stretched out it is.. I took some pics and will add them after breakfast.. yuckie thing!