Although the exact form of the larvae differ among the echinoderm groups, all are bilaterally symmetrical. In the sand dollar larva below, you can draw a line of symmetry through the middle of the picture. read more
The body plan of echinoderms undergoes a fundamental shift during development. All echinoderms have secondary radial symmetry; that is, they are bilaterally symmetrical during larval development but become radially symmetrical as adults. read more
Echinoderms exhibit secondary radial symmetry in portions of their body at some stage of life. This, however, is an adaptation to their sessile existence. They developed from other members of the Bilateria and exhibit bilateral symmetry in their larval stage. read more