Based on their radial symmetry and lack of a complete gut, the Echinodermata might be placed in or near the basal eumetazoans such as the Cnidarians.
Work Step by Step
This shows why we use multiple traits, especially embryonic development, to decipher the history of life. Any one trait can be misleading on its own. Embryonic development is especially useful in seeing connections between organisms since it comes early in the life of an organism when less time has occurred for misleading morphological differences to have formed.