What are these? I recently started this tank with all the substrate, wood, and plants out of a local river. The first week, I noticed one of these, then it disappeared. Now I can count 4, one of them on the glass. The "stalk" is about 1/8" and the "arms" are about 1/4" from the top of one arm to the tip of the opposite.
What are they? They remind me of aiptasia...?