Plate from 18th century encyclopedia showing illustrations of various echinoderms, or fossil sea urchins. The group called cidaris (cidares) is a genus of pencil sea urchins. The group below are bilaterans. Their early larvae have bilateral symmetry, but they develop fivefold symmetry as they mature. This is most apparent in the "regular" sea urchins, which have roughly spherical bodies, with five equally sized parts radiating out from their central axes.