When you look at the first picture let me point out that this is a California Skate. I believe it's considered to be a type of Ray. There are two in the picture, both against the glass, one with it's back facing the camera and the other with it's underbelly. They were about 4-6 inches long not including the tail.
When I first saw this thing in the bottom corner of the tank and looked at it's underbelly (the one closest to the camera), the first thing I thought was Casper the ghost but almost as soon as I thought that it was replaced with the thought, "Oh my goodness, that looks just like a face!"
The more I looked at through the lens as I snapped the eerier (is that a word) it seemed and still it just fascinated me. I don't know if those are actually eyes and a mouth but that's what they look like to me!
My only regret about these pics are the scratches on the glass of the tank. I was going to edit them out but didn't want to mess up any of the real detail of this Skate.