Original: Physiology Echinoderms evolved from animals with bilateral symmetry; although adult echinoderms possess radial symmetry, echinoderm larvae are ciliated, free-swimming organisms that organize in a bilaterally symmetric fashion that makes them look like embryonic chordates.
Simplified: Echinoderms' larvae (babies) are ciliated free-swimming organisms that organize in a bilaterally symmetric fashion that makes them look like embryonic chordates.