These both belong to the Radiata division, however this is supposedly inaccurate due to the form of the echinoderms. I was wondering why? Apparently its something to do with different types of radial symmetry. Thanks.
Cnidarians and echinoderms?
Cnidarians are very primitive organisms, and echinoderms are much more derived. This is the simplest point of the problem. To get more advanced, the echinoderms have actually secondarily derived a radial symmetry from a bilateral one (their larvae are bilateral). Furthermore, not all echinoderms are even really radial (ex: sea cucumbers). But most importantly of all, cnidarians are protostomes and echinoderms are deuterostomes. This reflects very fundamental differences in development. Protostomes have determinate cell types, divide radially, and have the blastopore form the mouth. Deuterostomes have indeterminate cell tyes (stem cells), and generate the anus from the blastopore or another opening, but never the mouth.
I hope this helps.
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