The arthrodial membrane is a thin and flexible type of cuticle that inserts at the edge regions of neighbouring rigid skeletal elements creating a flexible connection. In the present study, we analyzed the structure, mineral composition, calcite organization and local stiffness and hardness of edge regions that form transitions to the arthrodial membranes in the tergites of the desert isopod Hemilepistus reaumuri. For the transitions to the arthrodial membrane, the results show an increase in the thickness of the epicuticle at cost of the distal exocuticle and a calcite layer, an increase in the ratio of phosphorus to calcium and a decrease in the local mechanical properties. The posterior edge region contains an unusually large stack of unidirectionally oriented parallel fibrils projecting to the lateral sides. At the edge, it turns down into a long ventral cuticle overlapping an anterior part of the neighbouring tergite. It forms a thin arched gap between the tergites that can help reducing water loss through the arthrodial membrane and protects the arthrodial membrane upon predation. A thick ventral ridge near the transition to the arthrodial membrane carrying bristles can prevent sand grains from access to the arthrodial membrane. From the dorsal cuticle to the transition to the arthrodial membrane, calcite units become larger and single crystalline turning their c-axes orientation perpendicular to the sagittal section plane. Comparison with edge regions of the beach isopod Tylos europaeus reveal common characteristics of the edge region, but also specific adaptations to the desert habitat of H. reaumuri.

中文翻译：

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沙漠等足类动物 Hemilepistus reaumuri 的边缘区域：从硬角质层到柔性关节膜的过渡

关节膜是一种薄而柔韧的角质层，插入相邻刚性骨骼元件的边缘区域，形成柔韧的连接。在本研究中，我们分析了沙漠等足类动物 Hemilepistus reaumuri 的 tergites 中形成过渡到关节膜的边缘区域的结构、矿物成分、方解石组织以及局部刚度和硬度。对于向关节膜的过渡，结果显示上表皮厚度增加，代价是远端外表皮和方解石层，磷与钙的比例增加，局部机械性能下降。后缘区域包含异常大的单向定向平行原纤维堆叠，突出到侧面。在边缘，它变成了一个长的腹侧角质层，与相邻白蚁的前部重叠。它在 tergites 之间形成一个薄的拱形间隙，可以帮助减少通过关节膜的水分流失，并在​​捕食时保护关节膜。靠近带有刷毛的关节膜过渡处的厚腹脊可以防止沙粒进入关节膜。从背侧角质层到关节膜的过渡，方解石单元变得更大，单晶将其 c 轴方向垂直于矢状截面。与海滩等足类动物 Tylos europaeus 的边缘区域的比较揭示了边缘区域的共同特征，以及对 H. reaumuri 沙漠栖息地的特定适应。