What structural feature is common among members of the Phylum Echinodermata?

Members of the Phylum Echinodermata are characterized by their unique structural feature of radial symmetry, particularly in their adult forms. This means that their bodies are organized around a central axis, allowing for a symmetrical arrangement of body parts that radiate from the center. This radial symmetry is especially evident in species such as sea stars, sea urchins, and sea cucumbers.

In contrast, larval stages of echinoderms exhibit bilateral symmetry, which later transforms into the adult's radial symmetry as they mature. The adult forms of echinoderms are adapted to their typically sessile or slow-moving lifestyles on the ocean floor, where this symmetry offers advantages in interacting with the environment, such as feeding and movement.

The presence of a chitinous exoskeleton, jointed appendages, or bilateral symmetry are features associated with other animal phyla, thus highlighting the distinct evolutionary path of echinoderms that led to their specific adaptations and structural characteristics.