Looks to be some kind of Toadstool but I could be wrong.
To post your own thread go into Saltwater and Reef identification Forum section then you should see a little button named “New Thread” click on that button.
This will open a new thread for you to enter your own thread. Click in the box name Title and enter your own title then click in the large box below and start typing and you already know how to post pictures in the threads.
So there you go…