1. Sacculina is a genus of barnacles that is a parasitic castrator of crabs. They belong to a group called Rhizocephala. The adults bear no resemblance to the barnacles that cover ships, whales, and piers; they are recognised as barnacles because their larval forms are like other members of the barnacle class Cirripedia. The prevalence of this crustacean parasite in its crab host can be as high as 50%. == Habitat == Sacculina live in a marine environment. During their larval stage they are pelagic, but as they form into adults they live as ectoparasites on crabs. Their primary host is the green crab, which is native to the Eastern Atlantic Ocean. Though these crabs have spread to other bodies of water, it is not believed that Sacculina barnacles have traveled with them to these new localities. == Anatomy == The body of the adult parasite can be divided into two parts: one part is called the "externa" where the bulbous reproductive organ of the parasite sticks out of the abdomen of the host... from wikipedia.org