Junk, sand sifting stars are not as harmfull to sandbeds as some of the other critters mentioned, other than the fact that they disturb a good deal of sand. The problem with the sand sifting stars is that they usually starve in a few months because they run out of food. There are all sorts of sand critters that will tend to your sand bed, bristle worms, great scavengers, various other worms that I dont know the name of

some common names are spaghetti worms, medusa worms, these worms live in the sand and feed on detritus and scanvenge uneaten food, pods will eat detritus and some feed on algae, tiny starfish like mini brittles will feed on detritus, nassarious snails will also. You want to be able to look at your sand and see varrious worm trails and critters against the glass, that is if you sand bed is deep enough to support them, at least 4". All these critters will not only stir you sand in search of food, but to an extent,depending on the fish you have, will provide a live food source as well. If you have a lot of fish that will feed on the critters, wrasses, dragonets, ect. then youll want a refugium, either in the tank or connected to, in which these guys can breed. I have a ton of critters in my sand and most of them came from my live rock, you can also buy them online, and getting handfulls of sand from other reef tanks is a good way to seed your sand also. With a live sand bed you want critters cleaning and stirring it, but you dont want anything to big thats going to disrupt the low oxygen zones, gobies, large burrowing starfish and other larger critters can affect the effectivness of your sand bed by introducing oxygen into these low to no O2 zones thus killing the critters and bacteria that dwell there. I had a fiji sand star about a year ago, he did great for a couple of months, then all of a sudden he was in the open a lot more, I think he was searching for food, then he began to lose limbs and died. Most large stars that cannot be hand fed and must feed on food int he sand will die, some may make it in very large tanks, but most dont keep tanks with enough sand surface to support them. HTH