Adult echinoderms have radial symmetry, and sea urchins are echinoderms, in the same family as starfish. Given these facts, what has radial symmetry among the following options:
- peachleaf willow
 - sea urchins
 - humans
 - gastropod shells
 - A Greek letter
 - asymmetry
 - dogs
 - Most plants


 

  sea urchins       