Since you have a bit of aggressive fish, you can take your chance on getting a decent size horseshoe crab, but you will have to stay cautious. Or: recently I bought a Red Coris Wrasse. Amazing and Beautiful!!!! They are kind of ugly as juveniles, but become one of the most amazing looking fish as they mature. They do a great job sifting the sand. They are considered aggressive, so you don't have to worry about it getting picked on. They borrow in the sand to sleep. It fascinating watching them go in, and just as cool to watch them come out to feed. One of the best fish I've ever purchased. I will send a pic of mine. The colors at that of a Harlequin Tusk.
Red Coris Wrasse( even more beautiful in person)