The tube feet are filled with seawater, which the sea star brings in through the madreporite (a sort of trap door) on its top side. According to the National Ocean Service, adult sunflower sea ...

This is genital plate 2, also known as the madreporite plate. It is densely perforated by minute pores, which are the openings to the water vascular system, and is perforated at its edge by up to five ...