What's this star looking thing on my glass? cleaned some rocks yesterday and they popped out overnight

[reefo420]

i had some webs coming from glass to a rock, thought it was a snail but i couldn't find anything, undermicroscopeg..etc, cleaned the rock, put it back in and now these things are showing all over the left side of the tank, which has the lowest flow, what are they?

 

[Gtinnel]

Looks like hydroids

 

[homer1475]

New tank?

+1 hydroid jelly fish.

As the tank matures. they will die off. No idea where they come from, but they always seem to show up in new tanks.