Answer:
water-vascular system
Explanation:
Echinoderms exhibit several unique features and the presence of a water vascular system is one of them. The water vascular system of these organisms consists of a network of fluid-filled canals and chambers. The marine water enters and exits the system through an opening. This system functions as a hydrostatic skeleton during locomotion.
Tube feet of these organisms are filled with fluid as water enters into them via the canals of the water vascular system lead to them. This inflates the tube feet and serve in locomotion. The water entering through the water vascular system also brings in dissolved oxygen and food particles into the body.
