An alpheid shrimp digs and maintains a deep burrow. while underground, the shrimp is safe. above ground, it is vulnerable to predators. a goby fish lives in the burrow with the shrimp. the goby fish sits at the entrance, keeping watch for predators, and signals the shrimp with a flick of its tail when it is safe to come out. or, if a predator swims by, the goby darts into the burrow and the shrimp retreats further inside. these two animals are completely dependent on each other—the goby benefits by getting a burrow to live in and the shrimp knows when predators are near.