Elliptical Fourier shape analysis of sea urchin species in the family Echinometridae

A range of sizes of eight sea urchin species in the Family Echinometridae ( Echinostrephus aciculatus, Heliocidaris erythrogramma, Colobocentrotus atratus, Heterocentrotus mamillatus, Heterocentrotus trigonarius, Echinometra mathaei, Echinometra lucunter, and Echinometra vanbrunti ) were digitized and their shapes decomposed using elliptical Fourier analysis to quantify shape differences. Coefficients of sines and cosines of harmonics were used in a principal components analysis to show the separation of species. The principal component analysis shows the Echinometridae shape morphospace with the greatest separation of Echinostrephus and Colobocentrotus from other species. Major loadings were related to morphological measurements: height/diameter, lift of the oral surface above the substrate, and position of the ambitus to height. All species showed an increase in height/diameter with size, but only some species showed a correlation of oral lift or position of the ambitus with Fourier coefficients.