Question

Can someone help me out with this question please?

What does the bilateral symmetry of the bipinnaria larvae suggest about the ancestry of the sea stars, and perhaps of the echinoderms?

Answer 1

Echinoderms acquire various forms of symmetry. The pentameral is the main appearance and the other forms of symmetry are originated from it. Though the echinoderms ancestors, which originated in the Cambrian period, were supposed to be bilaterians, and the echinoderms ancestors, originated in the Cambrian era, were deuterostomes. And the deuterostomes are with bilateral symmetry, this can conclude that the echinoderms ancestors were bilaterians. After some time due to evolution, to become accustomed to their planktonic and benthonic habitat, echinoderms alter from bilateral to asymmetry, and then to pentameral symmetry because of 5 tails. The bipinnaria larvae of the echinoderm are bilateral at the stage of their early development. At the stage of embryonic development of sea urchins and starfish, the location and the developmental series of each arm are predetermined, entailing an auxological posterior/anterior axis. The Starfish also have the cluster of Hox gene, which directs the development of symmetry.