Benthic foraminifera, members of Rhizaria, inhabit a broad range of marine environments and are particularly common in hypoxic sediments. The biology of benthic foraminifera is key to understanding benthic ecosystems and relevant biogeochemical cycles, especially in hypoxic environments. Chilostomella is a foraminiferal genus commonly found in hypoxic deep‐sea sediments and has poorly understood ecological characteristics. For example, the carbon isotopic compositions of their lipids are substantially different from other co‐occurring genera, probably reflecting unique features of its metabolism. Here, we investigated the cytoplasmic and ultrastructural features of Chilostomella ovoidea from bathyal sediments of Sagami Bay, Japan, based on serial semi‐thin sections examined using an optical microscope followed by a three‐dimensional reconstruction, combined with TEM observations of ultra‐thin sections. Observations by TEM revealed the presence of abundant electron‐dense structures dividing the cytoplasm. Based on histochemical staining, these structures are shown to be composed of chitin. Our 3D reconstruction revealed chitinous structures in the final seven chambers. These exhibited a plate‐like morphology in the final chambers but became rolled up in earlier chambers (toward the proloculus). These chitinous, plate‐like structures may function to partition the cytoplasm in a chamber to increase the surface/volume ratio and/or act as a reactive site for some metabolic functions.

中文翻译：

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Chilostomella（有孔虫、Rhizaria）丰富的几丁质结构及其潜在功能


底栖有孔虫是根藻属的成员，栖息在广泛的海洋环境中，在缺氧沉积物中尤其常见。底栖有孔虫的生物学是了解底栖生态系统和相关生物地球化学循环的关键，特别是在缺氧环境中。 Chilostomella 是一种有孔虫属，常见于缺氧的深海沉积物中，其生态特征知之甚少。例如，其脂质的碳同位素组成与其他共存属有很大不同，可能反映了其代谢的独特特征。在这里，我们基于使用光学显微镜检查的连续半薄切片和三维重建，结合超薄切片的 TEM 观察，研究了来自日本相模湾深海沉积物的 Chilostomella ovoidea 的细胞质和超微结构特征。 TEM 观察揭示了细胞质中存在丰富的电子致密结构。根据组织化学染色，这些结构显示由几丁质组成。我们的 3D 重建揭示了最后七个腔室中的几丁质结构。它们在最后的室中表现出板状形态，但在早期的室中（朝向前室）卷起。这些几丁质的板状结构可能起到分隔室中细胞质的作用，以增加表面/体积比和/或充当某些代谢功能的反应位点。