Tardigrades (water bears) are microscopic invertebrates of which the anatomy has been well studied using traditional techniques, but a comprehensive three-dimensional reconstruction has never been performed. In order to close this gap, we employed X-ray computed tomography (CT), a technique that is becoming increasingly popular in zoology for producing high-resolution, three-dimensional (3D) scans of whole specimens. While CT has long been used to scan larger samples, its use in some microscopic animals can be problematic, as they are often too small for conventional CT yet too large for high-resolution, optics-based soft X-ray microscopy. This size gap continues to be narrowed with advancements in technology, with high-resolution imaging now being possible using both large synchrotron devices and, more recently, laboratory-based instruments. Here we use a recently developed prototype lab-based nano-computed tomography device to image a 152 μm-long tardigrade at high resolution (200–270 nm pixel size). The resulting dataset allowed us to visualize the anatomy of the tardigrade in 3D and analyze the spatial relationships of the internal structures. Segmentation of the major structures of the body enabled the direct measurement of their respective volumes. Furthermore, we segmented every storage cell individually and quantified their volume distribution. We compare our measurements to those from published studies in which other techniques were used. The data presented herein demonstrate the utility of CT imaging as a powerful supplementary tool for studies of tardigrade anatomy, especially for quantitative volume measurements. This nanoCT study represents the smallest complete animal ever imaged using CT, and offers new 3D insights into the spatial relationships of the internal organs of water bears.

中文翻译：

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水熊的 X 射线成像为缓步动物的内部解剖学提供了新的视角

缓步动物（水熊虫）是微观无脊椎动物，使用传统技术对其解剖结构进行了很好的研究，但从未进行过全面的三维重建。为了缩小这一差距，我们采用了 X 射线计算机断层扫描 (CT)，这是一种在动物学中越来越流行的技术，用于对整个标本进行高分辨率、三维 (3D) 扫描。虽然 CT 长期以来一直用于扫描较大的样本，但它在一些显微动物中的使用可能会出现问题，因为它们通常对于传统 CT 来说太小，而对于高分辨率、基于光学的软 X 射线显微镜来说又太大了。随着技术的进步，这种尺寸差距继续缩小，现在可以使用大型同步加速器设备以及最近基于实验室的仪器进行高分辨率成像。在这里，我们使用最近开发的基于实验室的原型纳米计算机断层扫描设备以高分辨率（200-270 nm 像素大小）对 152 μm 长的缓步动物进行成像。生成的数据集使我们能够以 3D 形式可视化缓步动物的解剖结构并分析内部结构的空间关系。身体主要结构的分割可以直接测量它们各自的体积。此外，我们单独分割每个存储单元并量化它们的体积分布。我们将我们的测量结果与使用其他技术的已发表研究的测量结果进行比较。本文提供的数据证明了 CT 成像作为研究缓步动物解剖学的强大补充工具的效用，特别是对于定量体积测量。