Hermit crab's anemone

Not only do hermit crabs use shells for protection, they will find a stinging anemone and place it on top of their shell (especially when their arch enemy octopi has a lair nearby). On this species of anemone you can sometimes find a small barnacle. The barnacle catches plankton that floats past like the anemone but every now and again it tears off and eats one of the anemone’s tentacles (sort of like having a hat that eats your hair).
Normanby Island, Frankland Islands, rock pools