I'd take out at least 1 tang both if you dont' have at least a 75 gal. I'd put the star in something so that you can keep a close eye on it. What's happened is that he's expeled his stomach from the center disk and the stuff from the legs are most likely the calcium bridges it uses to move etc. The other stuff is probably tissues from it's body ,"so not good". They do have some pretty good regenerative powers though and if some of the legs stay together they may grow new bodies ,"I honestly wouldn't count on it though," You'll have to keep your water absolutly pristine and hope it has enough fat stored to make it through and most recent imports just don't.
Brine isn't really a great food for fish it's more or less the pop corn of the marine world,"most people like it but they don't get much out of it."
What I do is go to the sea food counter and buy things like fish, shrimp in shell,oysters,squid, sushi wrappers, brewers yeast etc. lightly puree in the blender,"raw" add selcon or other vitamins and scoop it out into a dedicated ,"unless you really want a divorce," ice tray and freeze. That way I know what my critters are getting I can cut off as much or as little as needed and vary particle size for a lot of critters.
hth and best of luck