As you are walking along a beach, you find an animal and believe that it belongs to the class Asteroidea.

As you are walking along a beach, you find an animal and believe that it belongs to the class Asteroidea. Which of the following characteristics would support your hypothesis that the animal is a sea star and not another type of echinoderm?

A. It feeds on other animals

B. It has a hydrostatic skeleton, formed from its water vascular system

C. It is pentaradially symmetric

D. Its central region is not well delineated from its appendages

The correct answer is D. Please explain why this is the right answer and not A.