Just some info...
"Sand sifters - animals that sift sand to get food out of it. Sleeper gobies, etc. Also some burrowing sea stars.
These animals are sifting through the sand to eat the sand fauna that you want to maintain... bad news for the sand critters.
Burrowers are animals like burrowing sea cucumbers that move through the sediment and eat it. They eat off the bacteria and leave the sediment
The sediment is recolonized by bacteria and this growth stimulates the function of the biological filter.
So burrowers are good guys - burrowing sea cukes, sea urchins, some worms. The only problem is that if they are happy, you never see 'em.
Kinda hard to spend $$$ on animals you never see. But, it is a good investment.rs"
Quote from here,
http://www.reefs.org/library/talklog/r_shimek_090698.html