Mariner.....way back when, I had a few correspondances with Dr. Ron and he confirmed their predatory nature.....especially when they get big.....but, he really didn't have any first hand experience with their being that large. There actually is quite a bit of info on the net about them....but few first hand aquarium experiences.
Since this is my second round with them, I have been able to experience first hand by observing their behavior (a know your enemy thing). As many folks have expressed.....How can you miss something that large ? ...... Well, it's easy......they are so good about moving/living within rock that it took me about 9 hrs of nightime viewing before I spotted him. I would bet that many....and maybe even most.....reefers out there have one of these guys. I see several of them (tiny ones a few inches long) at the bottom of rock boxes when they're unloaded at the LFS each week.....at least the rocks from Fiji. I think that they are confused with being bristlworms when that size. Maybe I'm just unique in that, for whatever reason, they grow well in my system.
Why don't you remove yours ???