Zoological Institute, Russian Academy of Sciences, 1 Universitetskaya Embankment, St. Petersburg 199034, Russia.
Zoological Institute, Russian Academy of Sciences, 1 Universitetskaya Embankment, St. Petersburg 199034, Russia.
Micron. 2025 Jan;188:103728. doi: 10.1016/j.micron.2024.103728. Epub 2024 Oct 9.
Sperm ultrastructure has been successfully used in gastropod taxonomy and here we attempted to identify potential synapomorphies within the Hygrophila, a group of freshwater lung-bearing gastropods, by examining sperm morphology and ultrastructure in two hygrophilan species of the genus Choanomphalus Gerstfeldt, 1859 (Lymnaeoidea: Planorbidae): Ch. riparius (Westerlund, 1865) and Ch. rossmaessleri (A. Schmidt, 1851). The spermatozoa of both species, like those of other Hygrophila, are divided into a head with an acrosome and nucleus, a midpiece containing a mitochondrial derivative, a glycogen piece, and an endpiece. The acrosome consists of an apical vesicle and a lucent-cored pedestal, plugged basally by compact electron-dense material (acrosomal plug) and separated from the nucleus by a membrane-bound vesicle (basal cap). The midpiece bears apically four surface ridges and contains four glycogen-filled helices inside the mitochondrial derivative. The midpiece is separated from the glycogen piece by an annulus composed of electron-dense material at the tip of the mitochondrial derivative and a hollow cylinder, but the latter appears to consist of two fused structures, making the annulus essentially tripartite. Spermatozoa of the two species show interspecific differences: in Ch. rossmaessleri, the acrosomal plug lacks a stem and the midpiece ridges differ in size, while Ch. riparius has spermatozoa with a stemmed plug and equal-sized ridges. The results of this and earlier studies suggest that sperm ultrastructure can provide synapomorphies for hygrophilan groups at different taxonomic levels. The Lymnaeoidea, one of the two superfamilies of the Hygrophila, appears to be characterised by a lucent-cored acrosomal pedestal, multiple glycogen helices and a tripartite annulus. The presence of a basal plug in the acrosomal pedestal is a possible synapomorphy for the clade uniting Planorbini Rafinesque, 1815 and Segmentinini F.C. Baker, 1945. In Planorbini including the two species of Choanomphalus, the pedestal is separated from the nucleus by a membrane-bound basal cap, a feature readily distinguishing this tribe from Segmentinini and other Lymnaeoidea. The spermatozoa of the two Choanomphalus species differ from those of other Planorbini in having two nuclear keels instead of one, but this character may not be taxonomically reliable.
精子超微结构已成功应用于腹足纲分类学，在此我们试图通过检查淡水有肺腹足类 Hygrophila 属的两个 Choanomphalus 物种（Gerstfeldt，1859 年）的精子形态和超微结构来鉴定潜在的共形特征：Ch. riparius（Westerlund，1865 年）和 Ch. rossmaessleri（A. Schmidt，1851 年）。这两个物种的精子与其他 Hygrophila 的精子一样，分为头部（带顶体和核）、中段（含有线粒体衍生物、糖原片和尾部）。顶体由一个顶端囊泡和一个中空核心的基柱组成，底部由紧密的电子致密物质（顶体塞）堵塞，并通过一个膜结合的囊泡（基底帽）与核分离。中段顶部有四个表面脊，线粒体衍生物内有四个充满糖原的螺旋。中段与糖原片之间由线粒体衍生物末端的电子致密物质环和空心圆柱体组成，但后者似乎由两个融合的结构组成，使得环基本上是三部分的。这两个物种的精子表现出种间差异：在 Ch. rossmaessleri 中，顶体塞没有茎，中段脊的大小不同，而 Ch. riparius 的精子有带茎的顶体塞和等大小的脊。本研究和早期研究的结果表明，精子超微结构可以为不同分类水平的 Hygrophila 群体提供共形特征。Hygrophila 的两个超级家族之一的 Lymnaeoidea，似乎以中空核心的顶体基柱、多个糖原螺旋和三部分环为特征。顶体基柱中存在基部塞可能是将 Planorbini Rafinesque，1815 和 Segmentinini F.C. Baker，1945 联合在一起的分支的一个可能的共形特征。在包括这两个 Choanomphalus 物种的 Planorbini 中，基柱通过一个膜结合的基底帽与核分离，这个特征很容易将这个部落与 Segmentinini 和其他 Lymnaeoidea 区分开来。这两个 Choanomphalus 物种的精子与其他 Planorbini 的精子不同，它们有两个而不是一个核龙骨，但这个特征在分类上可能不可靠。
