Dendrophyllia or Tubastrea?

So I am torn on which this is. From what i understand a great deal of its identity can be found with the polyps open, but I have had this for a about 2 weeks or so and still have yet to see open polyps on it. It was sold as a sun coral (tubestrea) but I am not quite sure it isn't the other either.

So other than the ID on this guy, at what point do i need to worry about the polyps not opening?

 

Properly IDing between dendro's and tubastrea's is impossible without looking at the coral under a microscope. I used to have some identical to yours, never got a true ID, but believed it to be tubastrea.

Third link is one of my favorite articles on tubastrea and dendro's.

http://www.3reef.com/threads/nikon-d3100-macro-hungry-pink-sun-coral.151964/
http://www.3reef.com/threads/anyone-interested-in-pink-sun-coral-tubastrea-frags.150659/
http://www.advancedaquarist.com/2011/12/corals

 

From the photos I've seen looks more like at Dendronphyllia

 

BTW yours looks in pretty rough shape and 2 weeks of not feeding will definitely have an effect on their health, I would start feeding it ASAP.