The goby fish of various assorments like to pair up with varous pistol shrimp. Up to 20 varieties specifically to how they benefit each other. This symbiotic relationship, to me, is seen as a rich person and maid. The difference being is that the shrimp builds their home in most cases and maintains it. What the goby fish does is provide protection in the sense that the as the shrimp excavates the home from the silt and sand, the fish looks for predators. With specific tail flicks either up or down, or left to right the goby warns the shrimp of warning.
Not all gobies and shrimps share this bond. Only 130 varieties of goby home with about 20 variety of shrimp. Even then not all gobies get along with any of that type of shrimp. They find each other and have a sort of natural "this will work" moment. Also the goby fish may change type of shrimp companion depending on what their need is.
"The Symbiotic Relationship Between Gobies and Pistol Shrimp" The Fish Channel, Duerbaum Johannes, n.d. Web Sept. 2014