goby and shrimp partnership

Yellow watchman goby and pistol shrimp were from saltwaterfish.com. I bought them separately, not "a pair" (because a pair was more expensive). But the next day after they were introduced in the tank, they became partners. I also bought a bubble tip anemone and two clownfish (Amphiprion ocellaris) but the fish ignored the anemone. My 40-gallon tank is about 2 month old.

PRO: It is fun to watch them building their cave.

CON: I hardly see them since they are living in the cave.