Erik,
You may have a zoanthid eating polycheate worm. It's Eunid or something similar, can't remember and I don't have my books to reference. Shimek has some writings about it. Do a search. They can hang out unnoticed for years in a tank. They can get really big and ugly and nasty and show up in your dreams at night and then you can make a movie about it, and, and maybe get Sting to star in it - oh wait thats already been done --How's the pillow making thing going?