Peristaltic burrowing (A); with (C) and without (B) segmentation. The peristaltic burrowing wave (A) can be sustained in segmented worms (C) with less muscular involvement than in nonsegmented worms (B) because fluid pressure maxima are localized to a few segments. P_max maximal pressure in hydrostat; P_min minimal pressure in hydrostat; (Modified and redrawn from Turbeville, J. M. and Ruppert, E. E. 1983. Epidermal muscles and peristaltic burrowing in Carinoma tremaphoros (Nemertini): Correlates of effective burrowing without segmentation. Zoomorphology. 103:103-120.)