aiptasia or duster? Favia?

[Algaewarrior]

Try putting a filefish in there and see if it eats them.

 

[newave]

Some more clues to ID, at least for what I have recently had appearing in my tank:

- I don't have a light meant for growing coral (yet). Just basic LED that came with the 3 gallon Tetra Cube.

- They super, super quickly retract into their stem/tube (?) in response to light touch.

- They're popping up fast, 4 have appeared within a week. Not confined just one area of the tank, popped up on two separate "islands" of LR.

 

[zoablasto]

Probably a Xenia