What is "whale barnacle"

Whale barnacles are barnacles belonging to the family Coronulidae. Whale barnacles attach themselves to the bodies of baleen whales during the barnacles' free-swimming larval stage. Though often described as parasites, the relationship is an example of obligate commensalism, as the barnacles neither harm, nor benefit, their host. Whale barnacles that, through circumstance, are forcibly detached from their whale have been noted to experience apoptotic necrosis triggering the decline and eventual demise of the individual. A number of taxa formerly treated as subfamilies of Corolunidae are now considered separate families in their own right, including the turtle barnacles in the family Chelonibiidae.