A serpent star is reef safe will stir your sand and are really cool (but you won't see it much). How old is your tank??? You should have a mature tank to add these guys because they eat out of the sand bed.
chocolate chip starfish will eat coral. serpant stars are very interesting, cool looking, and hardy. they are a great starter starfish. with other types of stars you have to be careful with salinity.
i dropped a shrimp pellet by him and he would walk to it and it was neat to watch it scoop it up and put it in its mouth...you would see the shape of the pellet in its stomach (body)...