sentences:  Like other echinoderms, sea urchin early larvae have bilateral symmetry, but they develop five-fold 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.The mouth is at the base of the animal and the anus at the top; the lower surface is described as "oral" and the upper surface as "aboral".