The coelom is large and extends into each arm of the starfish. The lining of the coelom has cilia. These beat to circulate the fluid of the coelom. Food molecules diffuse or are actively transported from the wall of the pyloric stomach into the coelomic fluid. The churning of the fluid distributes food molecules to all parts of the starfish.
Digestive waste is eliminated through the anus.
Nitrogen waste is carried by amoebocytes that inhabit the coelomic fluid. The amoebocytes take the nitrogen waste to skin gills. From the skin gills, the nitrogen waste diffuses into seawater surrounding the starfish. Carbon dioxide waste also diffuses into sea water from the skin gills. The carbon dioxide waste is carried by the coelomic fluid to the skin gills.