Why do many echinoderms have five-part radial symmetry?

While the evolutionary success of radial symmetry in echinoderms is not yet fully understood, scientists have proposed that a pentamerous (five-part) arrangement of skeletal components provides greater structural strength to the animal's skeleton than other configurations, such as a three-rayed pattern.1

This five-part symmetry is a defining characteristic that emerges during metamorphosis, where it becomes superimposed upon the fundamental bilateral symmetry present in the larval stages. The pentamerous pattern is deeply integrated into the anatomy of most living echinoderms, manifesting in the arrangement of the water-vascular system, tube feet, muscles, and parts of the nervous system.12