bro,i also experience it b4 n i dip it with fresh water n after one week,it open up back nicely.but i dont know what is that.sometimes when my coral accidently fall on my prata,it gets hurt n the seleton is expose n the whiteish thing like fine worm start to come out from within the prata.but dont worry it will go off in due time.this is what i experience.mayb some other pros out there can give you more explaination.hope that the beloved prata will b ok,