The shell of two barnacles that had been living on a calico scallop, Argopecten gibbus, making the likeness of a face. The interaction between these two species represents the form of symbiosis known as commensalism where one member of the relationship benefits and the other is not effected either positively or negatively. In this case the barnacle benefits and the scallop is not affected. In some cases, however, a heavy load of barnacles could begin to harm a host, in which case the interaction may be more parasitic.