Heteronomous annulation

Heteronomous annulation is a characteristic of some arthropods. It means that segments are differentiated from one another, each having different form so as to serve a different function – for instance, using some limbs for walking and others for feeding.

The trait is first observed in the armoured lobopods.^[1] It is thought to be the precursor to segmentation in arthropods, and perhaps resulted from the need to produce serially repeated defensive structures (spines).^[2] It can be studied using homeotic genes. ^[1] It is believed to be a trait found in the most recent common ancestor of Panarthropoda.^[3]