The Water-Vascular System is a characteristic feature of which group?

• A. Mollusks
• B. Echinoderms
• C. Tunicates
• D. Vertebrates

Answer: (B)

The Water-Vascular System is a hydraulic network unique to echinoderms, used to move, feed, and interact with their environment. Water flows into the system through a madreporic opening, travels via a stone canal to a ring canal, then into radial canals along each arm. From these canals, tube feet protrude; by changing pressure, the feet extend or retract to grip surfaces, crawl, and help capture prey. This system also aids in gas exchange and diffusion across the body surface. Examples like starfish, sea urchins, and sea cucumbers rely on it for locomotion and feeding. It’s not found in mollusks (which use a muscular foot and mantle), tunicates (chordates with different feeding/hydro systems), or vertebrates (which have a closed circulatory system and distinct movement tools).