Aplacophora is a small enigmatic group of worm-like molluscs covered by sclerites. The general morphology of the posterior end, including the gonopericardial system, in many species is well studied using light microscopy. However, knowledge of the ultrastructure of this complex is fragmentary and many questions concerning the excretion of metabolites in this group still remain. The gonopericardial system of Chaetoderma nitidulum Lovén, 1844 (Caudofoveata) from the White Sea was studied using light microscopy and 3D reconstruction from a series of semi-thin sections. The ultrastructure of the gonopericardial system was described in detail for the first time. The gonopericardial complex consists of gonads connected to the pericardium by ciliated paired gonopericardioducts. The pair of gonoducts begins at the lateral sides of the pericardium and opens into the mantle cavity. Gonoducts consist of upper and lower parts that are morphologically differentiated. The walls of the upper gonoducts consist of cells that likely participate in the excretion of metabolites and reabsorption of useful substances. Lower gonoducts are bulk bags with a small cell wall, in which there is a ciliary tract, likely for the excretion of metabolites and reproductive products. Spermatozoa were found at different stages of development in different parts of the pericardium and gonoducts. On the basis of previously published and newly obtained data, the process of excretion by C. nitidulum is proposed.

中文翻译：

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Chaetoderma nitidulum Lovén, 1844 (Caudofoveata) 的淋病心包复合体的一般形态和超薄结构

Alacophora 是一小群神秘的蠕虫状软体动物，上面覆盖着硬骨。使用光学显微镜可以很好地研究许多物种的后端的一般形态，包括心包系统。然而，关于该复合物超微结构的知识是零碎的，关于该组代谢物排泄的许多问题仍然存在。使用光学显微镜和一系列半薄切片的 3D 重建研究了来自白海的 Chaetoderma nitidulum Lovén, 1844 (Caudofoveata) 的淋病心包系统。首次详细描述了淋膜心包系统的超微结构。性腺心包复合体由通过纤毛配对的性心包导管连接到心包的性腺组成。这对性腺从心包的侧面开始，通向套腔。性腺由形态上分化的上部和下部组成。上性腺管壁由可能参与代谢物排泄和有用物质重吸收的细胞组成。下生殖管是带有小细胞壁的散装袋，其中有一个睫状体，可能用于代谢物和生殖产物的排泄。在心包和性腺的不同部位发现了处于不同发育阶段的精子。在先前发表的和新获得的数据的基础上，提出了 C. nitidulum 的排泄过程。上性腺管壁由可能参与代谢物排泄和有用物质重吸收的细胞组成。下生殖管是带有小细胞壁的散装袋，其中有一个睫状体，可能用于代谢物和生殖产物的排泄。在心包和性腺的不同部位发现了处于不同发育阶段的精子。在先前发表的和新获得的数据的基础上，提出了 C. nitidulum 的排泄过程。上性腺管壁由可能参与代谢物排泄和有用物质重吸收的细胞组成。下生殖管是带有小细胞壁的散装袋，其中有一个睫状体，可能用于代谢物和生殖产物的排泄。在心包和性腺的不同部位发现了处于不同发育阶段的精子。在先前发表的和新获得的数据的基础上，提出了 C. nitidulum 的排泄过程。在心包和性腺的不同部位发现了处于不同发育阶段的精子。在先前发表的和新获得的数据的基础上，提出了 C. nitidulum 的排泄过程。在心包和性腺的不同部位发现了处于不同发育阶段的精子。在先前发表的和新获得的数据的基础上，提出了 C. nitidulum 的排泄过程。