SEGMENTAL UNITS AND SHAPE CONTROL IN CHILOPODA

In geophilomorph centipedes, the overall shape invariance does not mir ror the widespread variability in segmental composition (intra-and int erspecific, linked or not with sex differences). We have developed a m orphometric approach to this puzzling mismatch by studying allometric patterns in ontogeny and segmental patterns of metric traits of sterna and appendages, as well as through a comparative evaluation of morpho logical complexity. Comparisons of segmental patterns from individuals with different number of body segments (N) show that both the overall shape of the trunk and the segmental distribution of morphological ma rkers are independent from N. Therefore, segments per se are of little significance as homologues. In Clinopodes flavidus C.L. Koch, 1847 (G eophilidae), size and shape of the leg-bearing trunk are in allometric relationship to the size of the N-invariant terminal body parts; this relationship is independent from N, that is, size and differentiation of trunk structures are independent from the number of segments. In a macroevolutionary perspective, a quantitative approach to morphologic al complexity of metameric structures reveals both increases and decre ases in complexity of centipede trunk structures.