I've got a few snails, emerald crabs, and a brittle star. The crabs never seem to leave the rocks, the snails don't leave the glass (but they do a good job of keeping that clean at least), and the brittle star is a lazy sob that never leaves his cave until he smells food. I had a few peppermint shrimp that used to go and pick at the sand moderately, but the star eventually hunted them all down and ate them. So my sand is getting to be pretty dirty. I'm thinking maybe I'll try some coral banded shrimp, or Sally lightfoot crabs... something that won't be instant-dinner for my star. I don't have any corals to worry about, just assorted live rock and macro algaes, so what other crab/shrimp species would fit?