Dauphin Island Sea Lab, Dauphin Island, AL 36528, USA
Department of Marine Sciences, University of South Alabama, Mobile, AL 36688, USA.
J Exp Biol. 2018 May 22;221(Pt 10):jeb167759. doi: 10.1242/jeb.167759.
Peristaltic burrowing in muds applies normal forces to burrow walls, which extend by fracture, but the kinematics and mechanics of peristaltic burrowing in sands has not been explored. The opheliid polychaete uses direct peristalsis to burrow in beach sands, with kinematics consistent with the 'dual anchor system' of burrowing described for diverse organisms. In addition to expansions associated with a constrictive direct peristaltic wave, worms alternately expand the head region, which is separated by septa from the open body cavity, and expansible lateral ridges that protrude from the 10th setiger. Tracking of chaetae with fluorescent dye showed that the body wall advances while segments are thin, then stationary segments expand, applying normal forces to burrow walls. These normal forces likely compact burrow walls and serve as anchors. Perhaps more importantly, peristaltic movements minimize friction with the burrow wall, which would expand dilatant sands. Considerable slipping of worms burrowing in a lower-density sand analog suggests that this dual-anchor peristaltic burrowing may be limited to a narrow range of mechanical properties of substrata, consistent with the limited habitat of in a narrow swash zone on dissipative beaches.
在泥中蠕动挖掘时，蠕动会对挖掘壁施加正常力，这些壁会通过断裂来延伸，但在沙中蠕动挖掘的运动学和力学尚未得到探索。叶须虫使用直接蠕动在沙滩中挖掘，其运动学与为各种生物描述的“双重锚定系统”一致。除了与收缩性直接蠕动波相关的扩张之外，蠕虫还会交替地扩展头部区域，该区域与开放的体腔由隔膜隔开，并且可扩展的侧脊从第 10 个体节突出。用荧光染料跟踪刚毛显示，当身体变薄时，体壁会向前推进，然后固定的身体会扩张，对挖掘壁施加正常力。这些正常力可能会压实挖掘壁并充当锚。也许更重要的是，蠕动运动使与挖掘壁的摩擦最小化，这将使疏松的沙子膨胀。在低密度沙模拟物中挖掘的蠕虫大量滑动表明，这种双重锚定蠕动挖掘可能仅限于基质机械性能的狭窄范围，这与在消散海滩上狭窄的破浪带中的栖息地有限相一致。
