Yeah...Oyster... I bought a sun coral colony once completely covering what I thought was a rock....however every so often I would see or rather I thought I saw it move...for a long time I thought I was going stir crazy...or that I had some symptoms of cabin fever lol...I finally watched it move straight on instead of out the corner of my eye and realized this wasn't an ordinary rock... it ended up being a oyster... pretty cool suprise when I found out what it was.