The funny thing here is that the particular example is relevant, because sea stars and other echinoderms belong to the taxon Bilateria (look at their larvae!).

The funny thing here is that the particular example is relevant, because sea stars and other echinoderms belong to the taxon Bilateria (look at their larvae!). And it illustrates the difficulty you run into when you try to use morphology or other features to derive your taxonomy. Cnidaria are an interesting comparison, because they are radially symmetric but not members of Bilateria. They are among the closest relatives to Bilateria. (People may recall the article about Ctenophores that was posted recently, which are also not in Bilateria, and are actually much more distant, even from Cnidarians.)