Final answer:
Echinoderms in their larval state initially exhibit bilateral symmetry but develop secondary radial symmetry as they metamorphose into adults.a) Bilateral symmetry
Step-by-step explanation:
Echinoderms, such as sea stars, sand dollars, and sea urchins, exhibit modified radial symmetry in their adult stage. However, in their larval stage, echinoderms initially have bilateral symmetry. This means that their bodies can be divided into two equal halves along a single plane. As they metamorphose, they develop secondary radial symmetry. This change in symmetry is a result of their evolution from bilaterally symmetrical ancestors.