This is a first for me. I have had my tank going for many years without any sand sifting “fish” but I was recently given a Diamond Goby. Now I know they have been known in the past to have relationships with pistol shrimp. But mine seems to live in the same cave as my serpent star fish. During the day the Goby is out doing his sifting thing till it is startled. Then in the evening the star fish comes out of the same cave. I have also witnessed the goby sifting the sand right inside the cave and occasionally dumping sand on the starfish’s head. All the star fish does is wipe the sand off its head and goes about its business. Is this a normal phenomenon, or do I just have a weird fish?