Adult echinoderms have radial symmetry, and animals with radial symmetry lack an anterior and posterior end. Given these facts, which of the following does not have an anterior and posterior end among the following options:
- Adult mammals
 - Adult reptiles
 - Adult birds
 - Adult echinoderms
 - Earth orbiting the Sun
 - an erupting volcano
 - peachleaf willow
 - sensory neurons


 

    Adult echinoderms     