My wife noticed this clear jelly looking thing about 1/2 cm in length tracking along the back of our tank tonight. You can see track marks where he's gone up and down the glass cleaning it. While I couldn't see any tenticles, it reminded me a lot of this guy (Not actual photo, I know this photo is of a comb jelly) having two extensions off this butt:
What might it be? A Jelly? Sorry, but he is so small and transparent that I'm sure I can't get a photo. He does look like clear pflemn though, with shape....