You are purchasing Purple Barnacle clusters. Barnacles are crustaceans related to lobsters and crabs. They are completely marine creatures, starting in an active swimming larval stage and then becoming sessile (non-moving) suspension feeders during the adult stage. They use their feathery appendages to rhythmically beat plankton and detritus inside their shells for consumption. These purple barnacle clusters are perfect for saltwater aquariums, collectors of the natural world, planters for air plants and/or as a conversation piece.