Brown jelly, but you have to act fast this kind of infection can kill your coral very very fast (a day or 2).
Try to take it out of your tank so the brown jelly wont stick to another coral. Siphon the brown jelly before you move it and then do the the dip metoth maybe you can save your coral. but anyway the gionopota live term is about 1 year or 2. Its a beutifull coral but is really hard to keep. You should read a little before purch any kindof corals.
The brown jelly you can cosider it as a gangrene, is not a desess but it came in the joint of direferent factors as wounds whey you carry them, water parameters, stress, hungry, etc.