Animation showing evolution of trap-jaw
The animation shows the changes in form as the trap-jaw mechanism becomes more divergent from the ancestral form. The jaws (yellow) develop small projections that can latch onto the labrum (purple). The labrum changes from functioning as a sensor in the ancestral gripping jaw to acting as a latch in the trap-jaw. The muscles in the head that control the jaw and the labrum undergo large changes in structure.