The nudibranch Tritonia exsulans (previously Tritonia diomedea) is known to have behaviors and neurons that can be modified by perturbations of the Earth’s magnetic field. There is no definitive evidence for how this magnetic sense is used in nature. Using an exploratory approach, we tested for possible effects of magnetic perturbations based on underwater video of crawling patterns in the slugs’ natural habitat, with magnets of varying strength deployed on the substrate. For analysis, we used a paired comparison of tracks of animals between segments 25–50 cm distant from the magnets and segments of the same tracks 0–25 cm from the magnets, to determine whether any differences depended on the strength of the magnet. Most track measurements (length, displacement, velocity, and tortuosity) showed no such differences. However, effects were observed for the changes in track headings between successive points. These results showed that tracks had relatively higher heading variability when they moved closer to stronger magnets. We suggest that this supports a hypothesis that T. exsulans continuously uses a magnetic sense to help maintain straight-line navigation. Further specific testing of the hypothesis is now needed to verify this new possibility for how animals can benefit from a compass sense.

中文翻译：

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稀土磁体影响自然生境中的磁敏感Nudibranch Tritonia exsulans的运动模式。

Nudibranch Tritonia exsulans（以前是Tritonia diomedea已知具有可以通过扰动地球磁场来改变的行为和神经元。没有确切的证据说明这种磁感在自然界中是如何使用的。使用探索性方法，我们基于underwater的自然栖息地中爬行模式的水下视频，并在基板上部署了不同强度的磁体，对水下磁干扰的可能影响进行了测试。为了进行分析，我们使用了成对的比较动物轨迹的方法，这些动物轨迹与磁体之间的距离为25-50 cm，而相同轨迹的部分之间的距离为磁体0-25 cm，以确定是否有任何差异取决于磁体的强度。大多数轨道测量值（长度，位移，速度和曲折度）都没有这种差异。但是，观察到了连续点之间的航向变化的影响。这些结果表明，当轨道靠近更强的磁体时，它们具有相对较高的航向可变性。我们建议这支持以下假设：T. exsulans不断使用磁性来帮助保持直线导航。现在需要对该假设进行进一步的特定检验，以验证这种新的可能性，从而使动物如何从指南针感觉中受益。