The form of barnacle most commonly encountered by land-lubbing humans is the gray, volcano-shaped, stony type that can be found attached to piers, buoys and boat hulls around the world, but this is only one form that barnacles can take. They have a wide range of body plans, but one of the most bizarre is the rhizocephalan barnacle, which is an internal parasite in other crustaceans. They infiltrate and spread within the body of their host and even alter its behavior and appearance. Infected crabs can be detected by the external reproductive structure of the rhizocephalan that grows where the crab's own eggs would be. The crab cleans and cares for this growth as if it were its own.