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.
Oxygen diffuses into the coelomic fluid from sea water at the skin gills.
Surrounding the skin gills are pedicellaria, pincher-like structures that remove debris from the surface of the starfish and ensure that the sites of gas exchange are not covered or obstructed in any way. The Phylum Echinodermata includes four classes. Starfish belong to the Class Asteroidea. These animals have tapering arms. The number of arms ranges from 5-20, and all are carnivores.