mouth stuck

Came home today and my clownfish’s mouth was ajar (open) still is and it has a little white thing on it still eats just fine just not being active like normal I’ve posted the best picture I could get, any knowledge on what I should be doing would be greatly appreciated

I need some help/advice. I have a pair of Ocellaris clowns together, only fish in their tank which they have been in for almost 2 years together, nothing new has been added, no anemone, no change in foods, water parameters are well within the norm. My female is not doing great, her mouth seems...