In museum study, an adult sea star has no clear head end despite active feeding. The specimen or feature is best linked with:

Adult echinoderms have radial organization and lack strong cephalization. Their nervous system is arranged around a nerve ring and radial nerves rather than a head-centered brain. This MCQ belongs to the Echinodermata topic in Animal Diversity-I and is written to test concept understanding rather than memorized wording.