How can evolution explain body symmetry?

I'm not sure why (in terms of functional reason) starfish have penteradial symmetry, but evolutionary progress is not the 'other way round'. Instead, the fact that there is a bilateral embryo stage in starfish and other echinoderms points to a common ancestry with other animal phyla - the ancestor species originally had bilateral symmetry in its adult form, and penteradial symmetry is one of the many unique characters acquired in the millions of years since the last common ancestor of echinoderms and the other phlya.In fact, similarities in embryological development tell us that echinoderms are actually most closely related to chordates - (animals with a rudimentary backbone - fish, reptiles, mammals).Some links providing some basic background:Echinodermata
Palaeos: Page not foundThis message has been edited by gengar, 04-04-2005 05:43 PM