Final answer:
Sea urchins and sand dollars have radial symmetry, which means their bodies are arranged around a central point. This allows them to access their environment from all directions.
Step-by-step explanation:
Sea urchins and sand dollars have radial symmetry. This means that their bodies are arranged around a central point. They have multiple parts that are arranged in a circular pattern, such as the spines on a sea urchin or the petals on a sand dollar. Radial symmetry allows these organisms to access their environment from all directions.