Gas Exchange

Gas exchange is essential in Asteroidea as they, like most echinoderms, possess limited aerobic capacity (Ruppert et al. 2004). As a result echinoderms are sensitive to changes in oxygen availability (Ruppert et al. 2004).  Tube feet, which act as gills, are essential to ensure gasexchange occurs (Ruppert et al. 2004). Externally, the gills are ventilated with sea water and internally via coelomic fluid (Ruppert et al. 2004). Tube feet are responsible for supplying oxygen to the WVS however the papulae act as specialised gills for the perivisceral coelom, supplying oxygen to the gut, gonads and muscles (Ruppert et al. 2004). They are located on the aboral surface of all starfish and are differentiated from the tube feet by their lack of a sucker at the terminal end of the structure (Ruppert et al. 2004). In addition, papulae grow directly out of the perivisceral coelom, unlike tube feet (Ruppert et al. 2004).