The web series Jonathan Bird's Blue World has some fascinating footage of rather colorful hermit crab. She’s even got decorations on her shell! Well, they look like frills, but those are sea anemones, which are attached to her shell. They help protect the crab by scaring away predators, and in turn, she helps the anemones find food.
But what’s really neat is that when the hermit crab upgrades her shell, she keeps the anemones! Watch how she does it. -via reddit