Which of the following systems is found in echinoderms?

Q. Which of the following systems is found in echinoderms?
A. Nervous system
B. Excretory system
C. Respiratory system
D. System of internal skeleton
Answer: System of internal skeleton

A. Nervous system
B. Excretory system
C. Respiratory system
D. System of internal skeleton
Answer: System of internal skeleton