This was given to you? If it wasn't properly removed from its previous home, it may have damage to its foot. That WILL cause melting.
Low lighting will cause an anemone to reabsorb it's own tissue and shrink. An anemone is capable of starving for months before dieing. Heat, shock, or physical damage are likely culprits here.
Keep a close eye on it, they can recover from a lot, but I agree with the previous posters that it doesn't look good.
Someone stop me! Please! But... not just yet...
55 Gal Tropical FW
55 Gal Mixed Reef