Final answer:
Sea urchins and sand dollars have a larval stage called a pluteus larva.
Step-by-step explanation:
Sea urchins and sand dollars belong to the echinoderm class Echinoidea. They have a larval stage called a pluteus larva. The pluteus larva has a bilaterally symmetrical body plan with ciliated bands that help it swim and feed. The larva gradually undergoes metamorphosis to transform into the adult form, which exhibits radial symmetry.