5 Clear Mark for Review Sacculina carcini is a barnacle that attaches to the underside of the green crab. The barnacle finds a hole in the green crab's exoskeleton, then uses microscopic hairs to feed on nutrients from the green crab's blood. The barnacle also lays its eggs in the green crab reproductive system, which sterilizes the green crab. Which term describes the role of S. carcini in this relationship?