The echinoids
A)have five long,slender arms.
B)are enclosed in a test.
C)do not have tube feet.
D)have open ambulacral grooves.

Question

Quizplus · Accepted Answer

Echinoids, such as sea urchins, are enclosed in a hard, calcareous test that provides protection and support.

Answer: D 
 Echinoids have ambulacral grooves that are open to the environment and used for locomotion and feeding. Tube feet can be found in these grooves. They typically have more than five arms arranged in a radial pattern.

The Echinoids