Its no doubt suffering from malnutrition and starving to death. It looks like Fromia monilis which like many other starfish commonly for sale feed on sponges or other small sessile animals. In most cases only very large mature reef aquariums can provide enough of what these animals need to survive. Theres a bit of reading on them here
http://www.reefkeeping.com/issues/2004-12/rs/index.php
Sorry to be such a downer. I tried a linka starfish once and it died in much the same way that you are describing in my 2 year old 120gal tank.