Echinoderms show radial symmetry as adults and bilateral symmetry as larvae. Which statement is correct?

Echinoderms show radial symmetry as adults and bilateral symmetry as larvae. Which statement is correct?

• A. Adults radial; larvae bilateral
• B. Adults bilateral; larvae radial
• C. Both adults and larvae radial
• D. Both adults and larvae bilateral

Answer: (A)

Echinoderms undergo a developmental shift from bilateral larvae to radial adults. The larval stage is bilaterally symmetric, which fits a free-swimming, directional lifestyle. During metamorphosis, the body reorganizes into a radial plan around the central axis, and most adults display pentaradial symmetry. So the correct statement is that adults are radial while larvae are bilateral. The other possibilities conflict with the standard pattern, since the adult form is not bilaterally symmetric and the larval form is not typically radial.

Echinoderms undergo a developmental shift from bilateral larvae to radial adults. The larval stage is bilaterally symmetric, which fits a free-swimming, directional lifestyle. During metamorphosis, the body reorganizes into a radial plan around the central axis, and most adults display pentaradial symmetry. So the correct statement is that adults are radial while larvae are bilateral. The other possibilities conflict with the standard pattern, since the adult form is not bilaterally symmetric and the larval form is not typically radial.