That is your starfish starting to die. Mine is doing the very same though at times it looks like it will recover. I have had this same issue w/ my star for about a month and things seem to be normal (movement, oral disk in check) otherwise but I know any day it can go bad to worse. You probably know that keeping sea stars are very difficult even though the fromia is considered the most forgiving one. Have you had any salinity swings lately? Acclimation issues? If at any point (sea to distributor to LFS to you) the sea star is not acclimated properly, it may suffer.