Fact 1: Echinoderms lack respiratory and excretory systems.

Fact 2: Echinoderms are represented by the starfish.

Given the two facts above, answer the question "starfish lack what kind of system?" with the following options: 
- respiratory
 - critical organs
 - alveoli
 - heat or cold
 - hydration
 - Bodily water
 - food and shelter
 - frontal zones


 

 respiratory        