This slide shows a cross section through the arm of a starfish. Note the spines, pincer-like pedicellariae and hollow dermal branchiae (used for respiration) that project from the epidermis of the body wall.  Observe the many calcareous plates or ossicles that form part of the skeleton of the starfish. Two sets of digestive glands, or pyloric ceca, can be seen suspended in the coelom by extensions of the peritoneum called mesenteries, or septa. On the oral surface notice the tube feet that terminate in suckers.  Above and between the tube feet are the ambulacral ossicles that contain the radial canal that brings hydraulic fluid into the arm for powering the tube feet.  Below the radial canal is a the V-shaped radial nerve that controls the movement of the tube feet.