Two characteristics that are unique to echinoderms are that they have radial symmetry and a water vascular system. Echinoderms use a hydraulic system to operate their limbs, and this system helps them eat. Examples of echinoderms that have radial symmetry are starfish and sea urchins.
The fact that echinoderms are pentaradial, which means that their bodies have five planes of symmetry, distinguishes them from similar organisms in the Cnidarian phylum. According to Earthlife, echinoderms developed radial symmetry over a long period because the first echinoderms did not possess this body symmetry. When an echinoderm larva is born, it has bilateral symmetry and develops radial symmetry later in life.
Echinoderms live only in water. Therefore they use the water to carry out certain functions. The water vascular system of echinoderms begins at an external opening, also referred to as a madreporite. The madreporite connects to the stone canal, which connects to the ring canal. The ring canal is in the center and has canals that branch into each arm. Each canal connects to shorter canals that lead to a valve. This valve descends into the tube feet. The tube feet exit out of tiny holes in the exoskeleton and push water in and out of the holes like a vacuum.