As others have stated the bristle stars, and serpent stars won't sift, or dig around in the sand bed. Mine have been pretty good about going after any detritus on the surface though. If you decide to go with one, stay away from the green serpents. They're fairly effective fish hunters. I've had two smooth reddish brown ones in my main tank for awhile and just moved the larger one to the lionfish tank. Once I can catch the other one It's going in the octo tank, cause I want to get a blue-spot jawfish when they start showing up in the LFS again.
B