Phylum. Starfish belong to the phylum Echinodermata, which is the largest phylum without any members that live on land or in fresh water. Echinoderms have five-point radial symmetry as adults, but are bilaterally symmetrical as larvae. They have an endoskeleton consisting of calcareous plates that often include spines.upiterimages/Photos.com/Getty Images. Although fish and starfish both belong to the kingdom Animalia -- which is the largest division of taxonomic classification -- starfish lack a spine, and therefore belong to a different phylum than true fish.