Echinoderms have a unique water vascular system with tube feet, and each starfish arm is lined with tube feet. Given these facts, what phylum do starfish belong to among the following options:
- fertile
 - animals
 - Echinoderm.
 - Mollusca.
 - Sponge.
 - Absorb light
 - Annelid.
 - a fish


 

   Echinoderm.      