A Crown Prince or Crown Princess is the heir or heiress apparent to the throne in a royal or imperial monarchy. The wife of a crown prince is also titled crown princess. In Europe, lineal succession conventions usually dictate that the eldest child (as in Sweden, Belgium, Norway and the Netherlands) or the eldest son of the current monarch (Spain, United Kingdom, Denmark) fills this role as Crown Prince or Crown Princess..
Hydrostatics is the branch of fluid mechanics that studies incompressible fluids at rest. It encompasses the study of the conditions under which fluids are at rest in stable equilibrium as opposed to fluid dynamics, the study of fluids in motion.
Hydrostatic skeletons, also known as hydroskeletons, are found in organisms with soft bodies, such as earthworms, spiders, jelly fish, sea anemones and star fish. When the organism dies, the pressure is no longer maintained and the body curls.