Barnacles are small hardy crustaceans that attach themselves permanently to a hard substrate, including the carapace of sea turtles. Loggerhead turtle (Caretta caretta) with barnacles on its shell.

Different species of algae, and a large variety of sessile and vagile animals may be found fixed on sea turtle´s shell and soft tissues. To get rid of these organisms, sea turtles allow tropical fishes to feed on the epibionts, in a mutually beneficial association, called “cleaning symbiosis”.