Percebes

Goose barnacles, also called percebes or turtle-claw barnacles or stalked barnacles or gooseneck barnacles, are filter-feeding crustaceans that live attached to hard surfaces of rocks and flotsam in the ocean intertidal zone. Goose barnacles formerly made up the taxonomic order Pedunculata, but the group has been found to be polyphyletic, with its members scattered across multiple orders of the infraclass Thoracica. Some species of goose barnacles such as Lepas anatifera are pelagic and are most frequently found on tidewrack on oceanic coasts. Unlike most other types of barnacles, intertidal goose barnacles depend on water motion rather than the movement of their cirri for feeding, so are found only on exposed or moderately exposed coasts.

Source: Wikipedia