not bashing you in anyway, but expect a lot of criticism for buying livestock with out first researching
The Sand Sifting Sea Star or Starfish, has a thick, beige to brown body with lateral spines (teeth) extending upward along each side of its five arms. With the help of these spines, it moves over the sandy bottom of the ocean sifting through sand for food. The spines also enable it to burrow into the sand to hide or digest its food.
It is very active and effective at moving large amounts of sand as it searches for food. They are omnivores and are great for reef aquariums for eating detritus and left over food. It does well in an aquarium setting if provided with a large, deep (several inches) sand bottom where it can feed and hide. It should not be housed with Puffers.
The Sand Sifting Sea Star is very intolerant of sudden changes in oxygen levels, salinity and pH of the water, and cannot tolerate copper-based medications. The drip acclimation method is highly recommended for all Sea Stars due to their intolerability to changes in water chemistry. It should never be exposed to air while handling.
Breeding in an aquarium is extremely difficult with no distinguishing characteristics to help differentiate males from females.
In the aquarium, it can be fed small pieces of shrimp, fish, urchins, bivalves, or other small starfish.
Care Level: Easy
Tank Conditions: 72-78°F; sg 1.023-1.025; pH 8.1-8.4; dKH 8-12
Max. Size In Aquarium: Up to 1'
Color Form: Brown, Tan
Temperament: Peaceful
Reef Compatible: Yes
Diet: Omnivore
Origin: Fiji, Tonga
Family: Astropectinidae
http://www.liveaquaria.com/product/prod_Display.cfm?pCatId=572
i would suspect it will need a larger tank eventually, due to the fact that its max size is as wide as your tank is with out anything in it... it might get a bit cramped with the LR in there