The Sad Truth

Recent studies have shown that sea urchins have photoreceptors around the tips and base of the tube feet....cool.  They have genes that code for opsin which has function in the human retina.  This is not too surprising since echinoderms are relatively close relatives of the chordates....us.  We share some developmental traits with the Echinoderms...sea cucumbers, sea stars, sea urchins, etc.  Among the invertebrates there are only about 6 groups that share our development strategy out of some 30 phyla.  We are deuterostomes as opposed to the rest of the lot who are protostomes.  If you have forgotten your developmental biology that means:  Initially development from a single fertilized cell develops into a tiny ball of cells called a blastula. Soon a little dimple develops on the ball and pushes inward forming the gut....in protostomes this little dimple becomes the mouth (Protostome = mouth first) later an anus will form.  In deuterostomes (mouth second) the dimple becomes the anus and only later does the mouth form.
Echinoderms and Chordates are deuterostomes....which leads us to the SAD TRUTH.