diplosegments

Diplosegments are a distinctive metameric unit of millipedes (Diplopoda). Each diplosegment arises when two successive embryonic body segments fuse during development, producing a single, double-length segment. A typical diplosegment bears two pairs of walking legs, one pair associated with each of the two fused segments. As a result, millipedes often have many legs but fewer apparent body segments than there are embryonic segments.

In anatomical terms, the diplosegments form a continuous series along the trunk, with dorsal tergites and ventral sternites aligned across the fused units. This fusion contributes to the characteristic rounded body shape and the slow, undulating gait observed in many species.

The concept of diplosegments is of taxonomic and evolutionary significance within Diplopoda. Variation in the number and arrangement of diplosegments among different groups provides useful characters for distinguishing families and genera. While the exact pattern can vary across lineages, the core feature remains the fusion of paired embryonic segments into single diplosomites bearing two pairs of legs.

In summary, diplosegments describe the fundamental segmentation plan of most millipedes, representing fused pairs of segments that give rise to two pairs of legs per apparent body segment and shape the distinctive diplopod body plan.