Banded Serpent Starfish
Serpent starfish come in a few different colors and styles, and all of them are a good choice as part of your cleanup crew. They will retreat into the rockwork most of the time, but surely will be seen when food hits the water. This banded starfish has been with me for more than six years. I have a pair of tan-brown ones since 2004, so 14 years at the time of this entry. They don't prey on fish or other invertebrates, and help keep the surface sand devoid of waste. I'd recommend one in a 30-60g tank.