Barnacle
Barnacles are suspension feeders, sweeping small food into their mouth with their curved 'feet'. They are cemented to rock (usually), and covered with hard calcareous plates, which they shut firmly when the tide goes out. The barnacles reproduce sexually, and produce little nauplius larvae which disperse in the plankton. Eventually, the larvae change into cypris form, and attach on other hard surfaces to form new barnacles. Their comparative anatomy was worked out in detail by Charles Darwin.