The external outline of ostracodes genera: one equation. Application in subfamily of the Trachyleberidinae.

Mathematical modelling by Fourier analysis is a suitable morphological desc riptor, which allowed a rigorous quantification of ostracodes outline shape . Its application in Trachyleberidinae reveals its: (1) importance in the c haracterisation of the contour; (2) performance in the quantification of th e similarities and the differences between taxa and their interpretation in evolutionary terms. Thus two major trends can be proposed: the first trend with Cyrthereis seems to keep ancestral characters (plesiomorphies). The s econd trend with Platycythereis in opposite shows a morphological renewing.