Q: What is considered to be a unique feature of echinoderms?


Read this paragraph and choose the correct option from the provided answers:

A unique feature of echinoderms is their water vascular system. This is a network of canals that extends along each body part. In most echinoderms, the canals have external projections called tube feet (see Figure below ). The feet have suckers on the ends. Muscle contractions force water into the feet, causing them to extend outward. As the feet extend, they attach their suckers to new locations, farther away from their previous points of attachment. This results in a slow but powerful form of movement. The suckers are very strong. They can even be used to pry open the shells of prey.

 Choices:

- oil vascular system

- air vascular system

- iron vascular system

- water vascular system


A:
water vascular system