* Hermit crab benefits: The sea anemone provides protection for the hermit crab. The anemone's stinging tentacles deter predators from attacking the crab. The anemone also helps the crab camouflage itself and blend in with its surroundings.
* Sea anemone benefits: The hermit crab provides the sea anemone with mobility. By attaching itself to the crab's shell, the anemone can access new food sources and territories. It also gets to travel around without having to expend any energy itself.
In short, both the hermit crab and the sea anemone benefit from this relationship. This is why it's considered a mutualistic symbiosis.