Measuring morphological complexity of segmented animals: centipedes as model systems

In segmented animals it is possible to define morphological complexity as t he degree of morphological differentiation of segments. A quantitative meth od for measuring morphological complexity of segmental patterns was devised by McShea in 1992, who introduced three geometrical indices. Here, we intr oduce a new index of morphological complexity and emphasize the possible de coupling between segmentation and segment differentiation and illustrate di fferent patterns of variation within segmental series and how these could a ffect morphological evolution and evolvability. Concepts are illustrated by contrasting the segmental models of two groups of centipedes (Chilopoda): the elongate Geophilomorpha and the short-bodied Lithobiomorpha. A prelimin ary application of the new metric provides no evidence of macroevolutionary increase in morphological complexity of centipede segmental organization.