The evolution of segmentation of centipede trunk and appendages

The segmentation of centipedes is interpreted in the light of a biphasic mo del of segmentation (holomeric plus meromeric). The mid-body anomaly (e.g. in the alternating short and long terga, or in the sequence of segments wit h and without spiracles) is regarded as due to an early patterning of the e mbryo, occurring before the onset of meromeric segmentation and affecting a level within the fourth eosegment of the trunk. Comparisons with the Diplo poda suggest that genital structures such as millipede gonopods did probabl y develop originally at this spot, whose position remained marked even afte r the transition from a putatively progoneate to the current opisthogoneate condition of centipedes, perhaps following gene duplication and divergence of expression patterns of the paralogues. A new lower limit for the number of leg-bearing segments [27, in a male specimen of Schendylops oligopus (P ereira, Minelli & Barbieri, 1995)] is established for Geophilomorpha. Coevo lutionary trends involving the segmentation of the trunk, the segmentation of the appendages (especially the antennae), the postembryonic developmenta l schedule and the presence or absence of regeneration ability supports a r ecent view of the appendages as evolutionarily divergent duplicates of the main body axis.