It's a member of the fromia genus. Related species are sold under dozens of names such as pink star, marbled star, red and white, and sometimes just as fromia stars.
Little conclusive research on their diet but they appear to consist primarily on film algae and related microfauna. Best bet is just to have lots of surface area for grazing. Mine did well in a 55 until it got too curious about the bubble coral and got its arm eaten off.
Someone stop me! Please! But... not just yet...
55 Gal Tropical FW
55 Gal Mixed Reef