The madreporite opening to aboral surface is an extension of the A. enterocoel B. axocoel C. somatocoel D. hydrocoel Gas exchange in a sea star occurs through A. polian vesicles B. pedicellaria C. papulae D. all of the above The madreporite A. provides access to sea water for the water vascular system B. serves as a micropore filter C. is found on the aboral surface D. all of the above While feeding, the following organ of a sea star is protruded through the mouth A. pyloric stomach B. cardiac stomach C. digestive caeca D. radula.