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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]