Crab Hacker Barnacle

Sacculina carcini, commonly known as the crab hacker barnacle, is a species of parasitic barnacle in the family Sacculinidae and a parasitic castrator of crabs. Its most common host is the European green crab, whose natural range spans the coasts of Europe and North Africa. It attaches to the crab's abdomen and affects the crab's fitness and its suitability for human consumption.