The microanatomy and ultrastructure of the excretory system of an undescribed mesopsammic gastropod of the genus Hedylopsis have been examined by means of semithin serial sections, reconstructions, and transmission electron microscopy. The functional metanephridial system comprises a monotocardian heart with a single ventricle and auricle in a spacious pericardium as well as a single, large kidney. Podocytes in the auricular epicardium represent the site of ultrafiltration and formation of the primary urine, whereas the flat epithelium of the kidney with extensive basal infoldings, large vacuoles and the apical microvillous border indicates modification of the primary filtrate. Solitary rhogocytes (pore cells) represent additional loci of ultrafiltration with an identical fine-structure as those of the podocytes (meandering slits with diaphragms covered by extracellular matrix). The presence of podocytes situated in the epicardial wall of the auricle is regarded as plesiomorphic for the Opisthobranchia and is confirmed for the Acochlidia for the first time. Kidney and rectum both open into a small, yet distinct mantle cavity. Within the Acochlidia this condition represents a plesiomorphic character only known from one further Hedylopsis species until now. Special cells (here termed microvillous pit-cells) with a presumed absorptive function are interspersed between the epithelial cells of the mantle cavity. They are mainly characterized by a prominent invagination of the apical border with densely arranged, very large microvilli. The presence of a mantle cavity that has been lost in all other acochlidian genera supports the systematic placement of the Hedylopsidae at the base of the Achochlidia.

中文翻译：

---

Acochlidian 腹足动物（上鳃）排泄系统和地幔腔的显微解剖学、超微结构和系统意义

已通过半薄连续切片、重建和透射电子显微镜检查了一种未描述的 Hedylopsis 中足腹足动物排泄系统的显微解剖和超微结构。功能性后肾系统包括一个单心室心脏和一个宽敞的心包内的单心室和心耳，以及一个大的肾脏。耳外膜中的足细胞代表超滤和原尿形成的部位，而具有广泛基底折叠、大液泡和顶端微绒毛边界的肾脏扁平上皮表明原滤液的改变。孤立的 rhogocytes（孔细胞）代表了额外的超滤位点，具有与足细胞相同的精细结构（曲折的狭缝，隔膜被细胞外基质覆盖）。位于耳廓心外膜壁的足细胞的存在被认为是后鳃亚纲的拟形性足细胞，并且首次证实了耳蜗纲的足细胞。肾脏和直肠都通向一个小而明显的地幔腔。在 Acochlidia 中，这种情况代表了一种 plesiomorphic 特征，直到现在才从另外一种 Hedylopsis 物种中得知。具有假定吸收功能的特殊细胞（此处称为微绒毛坑细胞）散布在地幔腔的上皮细胞之间。它们的主要特征是顶端边缘明显内陷，排列密集，非常大的微绒毛。在所有其他蜗牛属中已经消失的地幔腔的存在支持了 Hedylopsidae 在 Achochlidia 基部的系统定位。