Fact 1: Echinoderms lack respiratory and excretory systems.

Fact 2: Lung mechanics and gas exchange are topics during study of the respiratory system.

Given the two facts above, answer the question "What do Echinoderms lack?" with the following options: 
- Lungs
 - Mass
 - oxygen
 - eardrum
 - gills
 - ovaries
 - Organs
 - Bodies


 

 Lungs        