cientists have been scratching their heads for some time on how echinoderms—ie, starfish, sea urchins, and other creatures with bodies split into five equal sections—evolved from the "bilaterally symmetric" body shapes, which feature two mirrored sides, that most other animals have. Adding to the confusion is that starfish begin life as larvae with twofold symmetry, then morph into their grown-up versions. Researchers found that genes switched on in the outermost layers of one particular type of starfish, known as Patiria miniata, matched genes in acorn worms and vertebrates that are activated in those creatures' heads. Thurston Lacalli of British Columbia's...
