If Echinoderms Are Radially Symmetrical,why Are They Considered Primitive Relatives

If echinoderms are radially symmetrical,why are they considered primitive relatives of cnidarians?

A) Echinoderms branched from cnidarians but are considered more advanced because they also gave rise to chordates.
B) The echinoderm larvae are originally bilaterally symmetrical but metamorphose into a radially symmetrical adult.
C) Radial symmetry is maintained as a primitive state by all animals in the embryonic stage and can appear anywhere.
D) Echinoderms are the most primitive of the deuterostomes and evolution begins in each group with radial symmetry.
E) Echinoderms have a five-sided bilateral symmetry that just appears to be radial.