i found these things in my tank, there are about this big : *
And crawl on the glass like a snail.. the kinda look like jellyfish haah
I can see a orange dot in the middle... WAAAY to small to get a pic... sorry
Could it possibly be a flat worm of some sort? Also if you have tunicates/sea squirts their larvae can look a bit like a jelly . It could also be the mobile phase of a hydriod etc. Hard to say for sure.