You are presented with the question "What phylum do starfish belong to?" and the following answer choices: 
- fertile
 - animals
 - Echinoderm.
 - Mollusca.
 - Sponge.
 - Absorb light
 - Annelid.
 - a fish

Now knowing that echinoderms have a unique water vascular system with tube feet and each starfish arm is lined with tube feet, choose the best answer.


 

   Echinoderm.      