The primary difference
between arthropods and echinoderms is their covering. Arthropods have a tough,
non-living outer shell called exoskeleton, which protect their soft bodies
while echinoderms have living endoskeletons, which develop within the deeper
skin or body tissues and act as their protective covering.
Secondary difference is
that most of the echinoderms live on water while arthropods are not.
