Need an ID please

[Tonkastoy]

Hi everyone. I don't post much but I do lurk the boards and thought this would be the best place to get some help IDing something I found in my tank today.
My tank has been up and running for over a year and I recently discovered that I had a Mantis shrimp living among my live rock. Today is the day that I decided to pull out the rock he is living in and get him out and find him a home. While doing so I came across a rock that had a very odd looking 'thing' on it. After much hastle I finally removed the creature from the rock he was living in and I have no idea what it is! It almost looks like some sort of budibranch but I can't find anything that remotely resembles this thing. It is tan and cream in color and moves much the same way as an octopus does. I don't want to put it back in my tank if it is harmfull and not knowing what it is has me kind of worried. I have taken some pictures of it and they can be found here:
http://photobucket.com/albums/v310/T...t=DSCF0016.jpg
The picture isn't the best and I will try to get some better ones. This thing is moving about the dish it is in like crazy!
Any help would be greatly appreciated. Thanks
ETA: Mantis Shrimp is still in the rock and refuses to come out. 1-mantis 0-Me