Swimming and sinking behavior by pelagic snails is poorly studied but is important in their ecology, predator-prey interactions, and vertical distributions. We used a low magnification, high speed stereophotogrammetry system to study the swimming and sinking kinematics of nine warm water pelagic snail species (seven thecosomes, one gymnosome, and one heteropod). As different thecosomatous pteropod species may have coiled, elongated, or globular shell morphologies, we focused on how the shell shape, body geometry, and body size affect their swimming behavior from a fluid mechanics perspective. In addition, ZooScan image analysis and metabarcoding of archived vertically stratified MOCNESS samples were used to relate swimming behaviors to night time and daytime vertical distributions. While different large scale swimming patterns were observed, all species exhibited small scale sawtooth swimming trajectories caused by reciprocal appendage flapping. Thecosome swimming and sinking behavior corresponded strongly with shell morphology and size, with the tiny coiled shell pteropods swimming and sinking the slowest, the large globular shelled pteropods swimming and sinking the fastest, and the medium-sized elongated shell pteropods swimming and sinking at intermediate speeds. However, the coiled shell species had the highest normalized swimming and sinking speeds, reaching swimming speeds of up to 45 body lengths s–1. The sinking trajectories of the coiled and elongated shell pteropods were nearly vertical, but globular shell pteropods use their hydrofoil-like shell to glide downwards at approximately 20° from the vertical, thus retarding their sinking rate. The swimming Reynolds number (Re) increased from the coiled shell species [Re ∼ O(10)] to the elongated shell species [Re ∼ O(100)] and again for the globular shell species [Re ∼ O(1000)], suggesting that more recent lineages increased in size and altered shell morphology to access greater lift-to-drag ratios available at higher Re. Swimming speed does not correlate with the vertical extent of migration, emphasizing that other factors, likely including light, temperature, and predator and prey fields, influence this ecologically important trait. Size does play a role in structuring the vertical habitat, with larger individuals tending to live deeper in the water column, while within a species, larger individuals have deeper migrations.

中文翻译：

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温水远洋蜗牛的游泳和下沉行为

远洋蜗牛的游泳和下沉行为研究很少，但在它们的生态学、捕食者-猎物相互作用和垂直分布方面很重要。我们使用低倍率、高速立体摄影测量系统来研究九种温水远洋蜗牛（七种蜗牛、一种裸体和一种异足类）的游泳和下沉运动学。由于不同的体型翼足类物种可能具有盘绕、拉长或球状的壳形态，我们从流体力学的角度关注壳的形状、身体几何形状和体型如何影响它们的游泳行为。此外，ZooScan 图像分析和存档的垂直分层 MOCNESS 样本的元条形码用于将游泳行为与夜间和白天的垂直分布联系起来。虽然观察到不同的大规模游泳模式，所有物种都表现出由相互附肢拍打引起的小规模锯齿状游泳轨迹。体壳的游动和下沉行为与壳的形态和大小有很强的对应关系，微小的卷壳翼足类动物的游动和下沉速度最慢，大型球状壳翼足类动物的游动和下沉速度最快，中等大小的细长壳翼足类动物的游动和下沉速度适中。 . 然而，卷壳物种具有最高的归一化游泳和下沉速度，达到高达 45 体长 s-1 的游泳速度。盘绕和拉长的壳翼足类动物的下沉轨迹几乎是垂直的，但球状壳翼足类动物使用它们的水翼状外壳以与垂直方向成大约 20° 的角度向下滑动，从而减缓了它们的下沉速度。游泳雷诺数 (Re) 从卷壳物质 [Re ∼ O(10)] 增加到细长壳物质 [Re ∼ O(100)]，再次对于球状壳物质 [Re ∼ O(1000)]，表明最近的谱系尺寸增加并改变了壳形态，以在更高的 Re 下获得更大的升阻比。游泳速度与迁移的垂直范围无关，强调其他因素，可能包括光、温度、捕食者和猎物场，影响这一生态重要特征。大小确实在构建垂直栖息地方面发挥作用，较大的个体往往生活在水柱的更深处，而在一个物种中，较大的个体有更深的迁徙。