what is this???

I have a friend with a 40 gallon tank. What I am aware she has in it, is an Angel fish, mollies, and rummy noses. I can find out more when I see her again. She found this in her tank, she and her husband are the only ones that are in their house, so they do not believe anyone put it in. It's the size of a marble it's semi-gelatinous it gives a little bit when you touch it, but it feels like if you cut it in half it would be solid all the way through. There is no nucleus like there would be if it were an egg. I have kept fish for many years and this is some thing I have never seen as I'm sure a lot of you have not, but I am looking for somebody who has or at least knows what this could be. Thank you ahead of time for any help you could be.

Only thing I can think of or close to it is a beneficial bacteria ball you can get as a 4 to 8 pack at the pet store. I have used them once and found one in my tank 2 months later and it had swelled up to about this size. Once they are in the water you cant see them and only way I found it was that it clogged my gravel vacuum.