What is the adult body symmetry of echinoderms?

• A. Bilateral
• B. Fivefold radial
• C. Radial
• D. Asymmetrical

Answer: (B)

Fivefold radial symmetry is the adult body plan of echinoderms. Their bodies are organized into five repeating sectors around a central axis, with five arms typically radiating from a central disk. This pentaradial arrangement is a hallmark of adult echinoderms, even though they start life as bilateral larvae and later adopt the radial form. While radial symmetry is the broader idea, specifying fivefold captures the common pattern seen in most adults. Descriptions like bilateral or asymmetrical don’t fit the typical adult layout.