Pentameral symmetry in echinoderms

Abstract

NICHOLS in his recent restatements1,2 of the suture-line theory, has made out a strong case for the adaptive significance of pentameral symmetry in the newly metamorphosed echinoderm. Its admittedly transient advantages at this stage, however, do not seem to account for a pentamerous form persisting to determine the symmetry of the adult body. There are exceptions - Nichols1 quotes Promachocrinus - but why are they not the rule ? © 1967 Nature Publishing Group.