Anemones will ALWAYS do two things when they die. Smell and disintegrate. Both are undeniable. Putting it in a cup is not a good idea, put him back in your tank (unless it is already too late). Don't let him (if you can) catch himself in the currents and be thrown all over the place. He sure doesn't look good, but anemones are very weird creatures and behave in strange ways. It is definitely hard to get them back to health if they are near dead though. Let's hope that your tank parameters are in reasonable shape, if he isn't dead. Let us know how it goes.