Scyphozoan Jellyfish

This is a photo of a Scyphozoan Jellyfish that is another hitchhiker in our tank. He's visible to the naked eye and swims with a pulsing motion just like an adult jelly. I've read several different sites on Scyphozoan Jellyfish and they say this one could grow to adult size if fed properly, but I've never seen one in my tank grow any larger than the size of the letter O. The fish seem to ignore them and I suppose they are to small to be a pest, so at this stage I'm going to leave them alone (not that I can get rid of them since I don't know where they are breeding in my tank.