I was watching it late last night, and was horrified when I saw the bowl with 2 gasping goldfish in it. They didn't look too good and were resting on the gravel bottom. I'll leave a link to show the type of thing they were enduring, shame on you big brother.
I'll add my 2p worth here and say they are hydroids, especially as you said there were tiny jellyfish like things in the tank before these appeared. Not sure which type they are though as there's 1000's HTH
Have had this shroom in my nano tank for just over a year now. It's only moved from it's original rock in the last week (changed position of powerhead and it didn't like it there anymore). I've had three others from it when its just moved its foot a little bit, which are in another tank. It's getting so big now I'm thinking of fragging it, but it just seems more barbaric the bigger it gets. Anyway show us your "big 1's" here if you will.
Ok, my daughter has just been using paint and now the settings are b######d. To write this I have got to put my head to one side because everything is vertical. When it's switched on the windows screen comes on as normal but once you log on everything goes from bottom of screen to top. It's a Dell DimensionE520. Hellllllllp