Get that sucker out of there! My Chocolate Chip Star tore my Pencil Urchin in two! And he also devoured my Serpent Star. I loved my Chocolate Chip Star, but not enough to feed him the other animals that I also loved.
But the behaviour you have described is, to my understanding, normal. Something to do with how fish tanks are not as deep as the sea.
I will try to find a good starfish site, too.
-Lynden