Multivariate analysis of the eight measured shell parameters. Results of the principal component analysis (PCA) based on the eight measured shell parameters. The PCA was done on a correlation matrix. The first three principal components axes account for about 80% of the total variation in shell morphology. Vectors of shell characters (length and direction compared to the PC axes) revealed that variation on PC1 is mainly associated with Dmx, WSC, NLb/OLb, FCI and UWI, PC2 with WER and IZR, and PC3 with WSC.