The Fine Structure of Mature Spermatozoa in Two Species of the Siphonariidae (Pulmonata : Basommatophora)

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Other Title
  • コウダカカラマツガイ科 2 種の精子の微細構造
  • コウダカカラマツガイ科2種の精子の微細構造〔英文〕
  • コウダカカラマツガイカ 2シュ ノ セイシ ノ ビサイ コウゾウ エイブン

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Mature spermatozoa from the seminal vesicle of the little hermaphroditic ducts of Siphonaria japonica and S. sirius were examined by using various techniques of light and electron microscopy. In S. japonica, the sperm averages 566.8μm in length, of which the helically twisted head occupies about 6.5μm including the 1.1μm acrosome, while that in S. sirius averages 766.6μm of which about 5.4μm is head. In the neck region, the conical structure is found at the basal concavity of the nucleus, and the cylindrical material lies posterior to it in both species. The coarse fibers are striated with a periodicity of 480Å in S. japonica and 380Å in S. sirius. The middle piece ensheathed by the mitochondrial derivative occupies 90-93% of the total length of the sperm in these two species. The axoneme at the anterior portion of the middle piece possesses a 9+9+2 pattern in the structure. Of the three mitochondrial ridges, one is primary helix containing glycogen granules and two others are secondary helices containing mitochondrial matrix. In the tail piece of both species, the peripheral axial filaments are surrounded by the glycogen granules. The end piece has only a 9+2 pattern. Systematically considered, the tail piece of Siphonaria has a feature common with those of the other Basommatophora. The characteristics of the neck region and the middle piece in Siphonaria is very similar to those in the terrestrial Stylom-matophora, differing from those in the fresh-water Basommatophora.

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