Barnacles are a type of crustacean related to crabs, lobsters, and shrimps. They are encrusters, attaching themselves temporarily to a hard substrate or a symbiont such as a whale, a sea snake, or another crustacean, like a crab or a lobster. Barnacles produce a cement-like substance that holds them fast to whatever surface they decide to adhere to as a larva. Once settled, a barnacle is attached to its place for life, attaching head-first. Although barnacles may look like mollusks with their shell-like covering, they are actually crustaceans. They feed through feather-like appendages called cirri, which comb the water for microscopic organisms. Barnacles secrete hard calcium plates that completely encase them, and most barnacles are hermaphrodites, meaning that they have both male and female sex organs.